Day 44 : array rotation - programming pearls

Author: mandliya

README.md

@@ -4,9 +4,9 @@
 
 | Current Status|     Stats     |
 | :------------: | :----------: |
-| Total Problems | 62 |
-| Current Streak | 43 |
-| Longest Streak | 43 ( August 17, 2015 - September 28, 2015 ) |
+| Total Problems | 63 |
+| Current Streak | 44 |
+| Longest Streak | 44 ( August 17, 2015 - September 29, 2015 ) |
 
 </center>
 
@@ -94,13 +94,16 @@ Include contains single header implementation of data structures and some algori
 | Implementation of Robin-Karp algorithm for string search | [robinKarpStringMatching.cpp](string_problmes/robinKarpStringMatching.cpp) |
 | Find next permutation of a given string, ie. rearrange the given string sucht a way that is next lexicographically greater string than given string | [next_permutation.cpp](string_problems/next_permutation.cpp)|
 
+### Common Data Structure and logic problems
+| Print the contents of matrix in a spiral order | [matrix_spiral_print.cpp](common_ds_problems/matrix_spiral_print.cpp)
+| Given a M x N matrix, rotate it by R rotations anticlockwise, and show the resulting matrix. | [rotate_matrix.cpp](common_ds_problems/rotate_matrix.cpp)|
+| Rotate an array by r elements ( left or right ) | [array_rotation.cpp](common_ds_problems/array_rotation.cpp)
+
 ### Math Problems
 | Problem | Solution |
 | :------------ | :----------: |
 |  Print all the permutations of a string. Example: Permutations of ABC are ABC, ACB, BCA, BAC, CAB, CBA | [string_permutations.cpp] (math_problems/string_permutations.cpp) |
 | Euclidean algorithm to find greatest common divisor of two numbers. (Iterative and recursive)|[gcd.cpp](math_problems/gcd.cpp)|
-| Print the contents of matrix in a spiral order | [matrix_spiral_print.cpp](math_problems/matrix_spiral_print.cpp)
-| Given a M x N matrix, rotate it by R rotations anticlockwise, and show the resulting matrix. | [rotate_matrix.cpp](math_problems/rotate_matrix.cpp)|
 
 ### Stack Problems
 | Problem | Solution |

common_ds_problems/array_rotation.cpp

@@ -0,0 +1,85 @@
+#include <iostream>
+#include <cassert>
+
+
+
+void swap( int & a, int & b)
+{
+    int temp = a;
+    a = b;
+    b = temp;
+}
+
+/**
+ * reverse an array from index 'start' to index 'end'
+ * @param arr   [The array]
+ * @param start [The start index]
+ * @param end   [The end index]
+ */
+void reverse( int * arr, int start, int end )
+{
+    while( start < end ) {
+        swap(arr[start], arr[end]);
+        ++start;
+        --end;
+    }
+}
+
+
+/**
+ * [leftRotate - rotate an array of length n with r rotations in left direction
+ * @param arr - the array
+ * @param n   - size of array
+ * @param r   - n number of rotations
+ */
+void leftRotate( int* arr, int n, int r )
+{
+    r = r % n;
+    reverse( arr, 0, r-1);
+    reverse( arr, r, n-1);
+    reverse( arr, 0, n-1);
+}
+
+
+/**
+ * [rightRotate - rotate an array of length n with r rotations in left direction
+ * @param arr - the array
+ * @param n   - size of array
+ * @param r   - n number of rotations
+ */
+void rightRotate( int* arr, int n, int r )
+{
+    r = r % n;
+    reverse( arr, 0, n-1);
+    reverse( arr, 0, r-1);
+    reverse( arr, r, n-1);
+}
+
+
+int main()
+{
+    int n, r, d;
+    std::cout << "Enter size of array :";
+    std::cin >> n;
+    std::cout << "Enter the contents of array:";
+    int * arr = new int[n];
+    for ( int i = 0; i < n; ++i ) {
+        std::cin >> arr[i];
+    }
+    std::cout << "Enter number of rotations you need:";
+    std::cin >> r;
+    std::cout << "Direction (left = 0, right = 1):";
+    std::cin >> d;
+    assert((d == 0) || (d == 1));
+    if ( d == 0 ) {
+        leftRotate(arr, n, r);
+    } else {
+        rightRotate(arr, n, r);
+    }
+    std::cout << "The array after rotation:\n";
+    for ( int i = 0; i < n; ++i ) {
+        std::cout << arr[i] << " ";
+    }
+    std::cout << std::endl;
+    return 0;
+}

math_problems/matrix_spiral_print.cpp renamed to common_ds_problems/matrix_spiral_print.cpp

@@ -4,6 +4,7 @@
  */
 
 #include <iostream>
+#include <cmath>
 
 struct Node {
   int data;
@@ -40,7 +41,7 @@ Node * mergePoint( Node * head1, Node * head2 )
   Node * ptr1 = ( len1 > len2 ) ? head1 : head2;
   Node * ptr2 = ( len1 > len2 ) ? head2 : head1;
   int i = 0;
-  while ( i < abs(len1 - len2) && ptr1 ) {
+  while ( i < std::abs(len1 - len2) && ptr1 ) {
     ptr1 = ptr1->next;
     ++i;
   }