Rotate by 90 degree

Problem Statement - link #

Given a square matrix of size N x N. The task is to rotate it by 90 degrees in anti-clockwise direction without using any extra space.

Your Task: You dont need to read input or print anything. Complete the function rotateby90() which takes the matrix as input parameter and rotates it by 90 degrees in anti-clockwise direction without using any extra space. You have to modify the input matrix in-place.

Expected Time Complexity: O(N*N)
Expected Auxiliary Space: O(1)

Examples #

Example 1:

Input:
N = 3 
matrix[][] = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
Output: 
Rotated Matrix:
3 6 9
2 5 8
1 4 7

Example 2:

Input:
N = 2
matrix[][] = [[1, 2], [3, 4]]
Output: 
Rotated Matrix:
2 4
1 3

Constraints #

• 1 <= N <= 100
• 1 <= matrix[i][j] <= 1000

Solutions #

class Solution{
    public:
    //Function to rotate matrix anticlockwise by 90 degrees.
    void rotateby90(vector<vector<int> >& matrix, int n) 
    { 
        // code here 
        for(int i=0; i<n; i++)
            for(int j=i+1; j<n; j++)
                swap(matrix[i][j], matrix[j][i]);
        for(int i=0; i<n/2; i++)
            for(int j=0; j<n; j++)
                swap(matrix[i][j], matrix[n-1-i][j]);
    } 

};