C Program for Program for array rotation
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
Method 1 (Rotate one by one):
leftRotate(arr[], d, n) start For i = 0 to i < d Left rotate all elements of arr[] by one end
To rotate by one, store arr[0] in a temporary variable temp, move arr[1] to arr[0], arr[2] to arr[1] …and finally temp to arr[n-1]
Let us take the same example arr[] = [1, 2, 3, 4, 5, 6, 7], d = 2
Rotate arr[] by one 2 times
We get [2, 3, 4, 5, 6, 7, 1] after first rotation and [ 3, 4, 5, 6, 7, 1, 2] after second rotation.
Method 2 (A Juggling Algorithm) :
This is an extension of method 2. Instead of moving one by one, divide the array in different sets
where number of sets is equal to GCD of n and d and move the elements within sets.
If GCD is 1 as is for the above example array (n = 7 and d =2), then elements will be moved within one set only, we just start with temp = arr[0] and keep moving arr[I+d] to arr[I] and finally store temp at the right place.
Here is an example for n =12 and d = 3. GCD is 3 and
Let arr[] be {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12} a) Elements are first moved in first set – (See below diagram for this movement)
arr[] after this step --> {4 2 3 7 5 6 10 8 9 1 11 12} b) Then in second set. arr[] after this step --> {4 5 3 7 8 6 10 11 9 1 2 12} c) Finally in third set. arr[] after this step --> {4 5 6 7 8 9 10 11 12 1 2 3}
Below is the implementation of the above approach :
C
// C program to rotate an array by // d elements #include <stdio.h> /* function to print an array */ void printArray( int arr[], int size); /*Function to get gcd of a and b*/ int gcd( int a, int b); /*Function to left rotate arr[] of size n by d*/ void leftRotate( int arr[], int d, int n) { int i, j, k, temp; /* To handle if d >= n */ d = d % n; int g_c_d = gcd(d, n); for (i = 0; i < g_c_d; i++) { /* move i-th values of blocks */ temp = arr[i]; j = i; while (1) { k = j + d; if (k >= n) k = k - n; if (k == i) break ; arr[j] = arr[k]; j = k; } arr[j] = temp; } } /*UTILITY FUNCTIONS*/ /* function to print an array */ void printArray( int arr[], int n) { int i; for (i = 0; i < n; i++) printf ( "%d " , arr[i]); } /*Function to get gcd of a and b*/ int gcd( int a, int b) { if (b == 0) return a; else return gcd(b, a % b); } /* 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; } |
Output :
3 4 5 6 7 1 2
Time complexity : O(n)
Auxiliary Space : O(1)
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