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‎All_Views_BinaryTree.cpp

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/// All Views Binary Tree
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/// Bottom View (Idea: Consider axis about root, left side -> -ve and right side -> +ve , use map to store the latest occurrence in that level)
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class Solution {
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public:
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vector <int> bottomView(Node *root) {
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vector<int> result;
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if(!root) return result;
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map<int,int> mp; /// Col, val
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queue<pair<Node*,int>> q;
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q.push({root,0}); /// Queue {Node and Level (-ve , 0, +ve}
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while(!q.empty()){
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int sz=q.size();
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for(int i=0;i<sz;i++){
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Node *temp=q.front().first;
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int level=q.front().second;
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q.pop();
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mp[level]=temp->data;
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if(temp->left) q.push({temp->left,level-1});
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if(temp->right) q.push({temp->right,level+1});
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}
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}
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for(auto it : mp){
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result.push_back(it.second);
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}
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return result;
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}
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};
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/// Top View (Idea: Consider axis about root, left side -> -ve and right side -> +ve , use map to store the first occurrence in that level by checking its already presence or not)
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class Solution
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{
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public:
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//Function to return a list of nodes visible from the top view
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//from left to right in Binary Tree.
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vector<int> topView(Node *root)
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{
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vector<int> result;
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if(!root) return result;
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map<int,int> mp; // col,val
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queue<pair<Node*,int>> q;
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q.push({root,0});
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while(!q.empty()){
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int sz=q.size();
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for(int i=0;i<sz;i++){
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Node *temp=q.front().first;
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int level=q.front().second;
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q.pop();
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if(mp.find(level)==mp.end()) mp[level]=temp->data;
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if(temp->left) q.push({temp->left,level-1});
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if(temp->right) q.push({temp->right,level+1});
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}
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}
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for(auto it : mp){
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result.push_back(it.second);
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}
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return result;
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}
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};
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/// Vertical Order Traversal (View) // Idea: Maintaining Map (ordered), keep pushing into the level and return into vector afterwards
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vector<int> verticalOrder(Node *root)
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{
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vector<int> result;
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if(!root) return result;
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map<int,vector<int>> mp; // col, vector
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queue<pair<Node*,int>> q; // Node, level
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q.push({root,0});
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while(!q.empty()){
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int sz=q.size();
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for(int i=0;i<sz;i++){
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Node *temp=q.front().first;
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int level=q.front().second;
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q.pop();
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mp[level].push_back(temp->data);
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if(temp->left) q.push({temp->left,level-1});
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if(temp->right) q.push({temp->right,level+1});
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}
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}
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for(auto it : mp){
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vector<int> temp=it.second;
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for(auto ele : temp){
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result.push_back(ele);
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}
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}
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return result;
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}
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/// Multiset and map based solution (Optimal)
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class Solution {
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public:
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vector<vector<int>> verticalTraversal(TreeNode* root) {
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map<int, map<int, multiset<int>>> nodes;
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queue<pair<TreeNode*, pair<int,int>>> q;
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q.push({root, {0,0}});
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while(!q.empty()){
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auto p=q.front();
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q.pop();
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TreeNode* node=p.first;
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int x=p.second.first, y=p.second.second;
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nodes[x][y].insert(node->val);
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if(node->left){
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q.push({node->left, {x-1, y+1}});
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}
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if(node->right){
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q.push({node->right, {x+1, y+1}});
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}
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}
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vector<vector<int>> ans;
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for(auto p: nodes){
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vector<int> col;
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for(auto q: p.second){
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col.insert(col.end(), q.second.begin(), q.second.end());
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}
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ans.push_back(col);
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}
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return ans;
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}
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};
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/// Left Side View (Idea: recursion, start from root, go to left->left , if not then only go left->right,
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class Solution{
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public:
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vector<int> leftSideView(TreeNode* root){
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vector<int> ans;
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helper(root, 0, ans);
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return ans;
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}
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void helper(TreeNode* root,int level,vector<int> &ans){
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if(root==NULL)
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return ;
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if(ans.size()==level)
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ans.push_back(root->val);
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helper(root->left, level+1, ans);
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helper(root->right, level+1, ans);
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}
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};
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/// Left Side View (Queue)
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class Solution {
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public:
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vector<int> rightSideView(TreeNode* root) {
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vector<int> res;
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if(!root)
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return res;
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queue<TreeNode*> q;
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q.push(root);
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while(!q.empty())
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{
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int n=q.size();
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for(int i=0;i<n;i++)
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{
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TreeNode * node = q.front();
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q.pop();
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if(node->right)
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q.push(node->right);
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if(node->left)
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q.push(node->left);
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if(i==n-1)
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res.push_back(node->val);
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}
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}
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return res;
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}
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};
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/// Right Side View (Idea: recursion, start from root, go to right->right , if not then only go right->left,
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class Solution {
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public:
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void helper(TreeNode *root, int level, vector<int> &result){
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if(!root) return;
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if(result.size()==level){
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result.push_back(root->val);
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}
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helper(root->right,level+1,result);
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helper(root->left,level+1,result);
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}
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vector<int> rightSideView(TreeNode* root) {
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vector<int> result;
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if(!root) return result;
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helper(root,0,result);
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return result;
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}
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};
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/// Right Side View (Queue)
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class Solution {
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public:
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vector<int> rightSideView(TreeNode* root) {
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vector<int> res;
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if(!root)
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return res;
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queue<TreeNode*> q;
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q.push(root);
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while(!q.empty())
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{
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int n=q.size();
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for(int i=0;i<n;i++)
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{
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TreeNode * node = q.front();
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q.pop();
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if(node->left)
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q.push(node->left);
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if(node->right)
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q.push(node->right);
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if(i==n-1)
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res.push_back(node->val);
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}
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}
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return res;
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}
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};
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/// Boundary View : (Idea : Combination of left side + leaf nodes + right side view)
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bool isLeaf(Node *root){
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if(!root->left and !root->right) return true;
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return false;
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}
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void addLeftBoundary(Node *root, vector<int> &result){
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Node *curr=root->left;
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while(curr){
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if(!isLeaf(curr)) result.push_back(curr->data);
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if(curr->left) curr=curr->left;
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else curr=curr->right;
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}
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}
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void addLeaves(Node *root, vector<int> &result){
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if(isLeaf(root)){
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result.push_back(root->data);
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return;
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}
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if(root->left) addLeaves(root->left,result);
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if(root->right) addLeaves(root->right,result);
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}
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void addRightBoundary(Node *root, vector<int> &result){
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Node *curr=root->right;
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vector<int> temp;
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while(curr){
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if(!isLeaf(curr)) temp.push_back(curr->data);
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if(curr->right) curr=curr->right;
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else curr=curr->left;
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}
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for(int i=temp.size()-1;i>=0;i--){
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result.push_back(temp[i]);
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}
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}
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class Solution {
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public:
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vector <int> boundary(Node *root)
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{
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vector<int> result;
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if(!root) return result;
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if(!isLeaf(root)) result.push_back(root->data);
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addLeftBoundary(root,result);
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addLeaves(root,result);
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addRightBoundary(root,result);
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return result;
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}
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};
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‎BinaryTree_BottomViewOrder.cpp

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/*
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Problem Statement: Given a binary tree, print the bottom view from left to right.
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A node is included in the bottom view if it can be seen when we look at the tree from the bottom.
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*/
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/// Bottom view (Binary Tree)
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//Function to return a list containing the bottom view of the given tree.
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class Solution {
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public:
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vector <int> bottomView(Node *root) {
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vector<int> result;
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if(!root) return result;
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map<int,int> mp;
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queue<pair<Node*,int>> q;
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q.push({root,0});
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while(!q.empty()){
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int sz=q.size();
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for(int i=0;i<sz;i++){
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Node *temp=q.front().first;
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int level=q.front().second;
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q.pop();
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mp[level]=temp->data;
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if(temp->left) q.push({temp->left,level-1});
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if(temp->right) q.push({temp->right,level+1});
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}
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}
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for(auto it : mp){
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result.push_back(it.second);
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}
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return result;
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}
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};

‎TheNightsWatch.cpp

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/// Nights Watch : Problem Code: WTCH // Codechef
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#include <bits/stdc++.h>
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using namespace std;
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int main() {
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int t;
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cin>>t;
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while(t--){
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int n;
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cin>>n;
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string str;
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cin>>str;
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// N Watchtowers -> 1 person , nighter's watch
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// Idea : Binary String with without consecutive 1's
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int counter=0;
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for(int i=0;i<n;i++){
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if(str[i]=='0' and (i==0 or str[i-1]=='0') and (i==n-1 or str[i+1]=='0')){
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str[i]='1';
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counter++;
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}
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}
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cout<<counter<<endl;
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}
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return 0;
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}
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