Write a function rotate(arr[], d, n) that rotates arr[] of size n by d elements.
Rotation of the above array by 2 will make array
Algorithm:
rotate(arr[], d, n) reverse(arr[], 1, d) ; reverse(arr[], d + 1, n); reverse(arr[], l, n);
Let AB are the two parts of the input array where A = arr[0..d-1] and B = arr[d..n-1]. The idea of the algorithm is:
Reverse A to get ArB. /* Ar is reverse of A */
Reverse B to get ArBr. /* Br is reverse of B */
Reverse all to get (ArBr) r = BA.
Reverse A to get ArB. /* Ar is reverse of A */
Reverse B to get ArBr. /* Br is reverse of B */
Reverse all to get (ArBr) r = BA.
For arr[] = [1, 2, 3, 4, 5, 6, 7], d =2 and n = 7
A = [1, 2] and B = [3, 4, 5, 6, 7]
Reverse A, we get ArB = [2, 1, 3, 4, 5, 6, 7]
Reverse B, we get ArBr = [2, 1, 7, 6, 5, 4, 3]
Reverse all, we get (ArBr)r = [3, 4, 5, 6, 7, 1, 2]
A = [1, 2] and B = [3, 4, 5, 6, 7]
Reverse A, we get ArB = [2, 1, 3, 4, 5, 6, 7]
Reverse B, we get ArBr = [2, 1, 7, 6, 5, 4, 3]
Reverse all, we get (ArBr)r = [3, 4, 5, 6, 7, 1, 2]
Implementation:
/*Utility function to print an array */ void printArray( int arr[], int size); /* Utility function to reverse arr[] from start to end */ void rvereseArray( int arr[], int start, int end); /* Function to left rotate arr[] of size n by d */ void leftRotate( int arr[], int d, int n) { rvereseArray(arr, 0, d-1); rvereseArray(arr, d, n-1); rvereseArray(arr, 0, n-1); } /*UTILITY FUNCTIONS*/ /* function to print an array */ void printArray( int arr[], int size) { int i; for (i = 0; i < size; i++) printf ( "%d " , arr[i]); printf ( "%\n " ); } /*Function to reverse arr[] from index start to end*/ void rvereseArray( int arr[], int start, int end) { int i; int temp; while (start < end) { temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; start++; end--; } } /* Driver program to test above functions */ int main() { int arr[] = {1, 2, 3, 4, 5, 6, 7}; leftRotate(arr, 2, 7); printArray(arr, 7); getchar (); return 0; } |
Time Complexity: O(n)
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