MockInterview:48. Rotate Image

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Note:

You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.

Example 1:

Given input matrix = 
[
  [1,2,3],
  [4,5,6],
  [7,8,9]
],

rotate the input matrix in-place such that it becomes:
[
  [7,4,1],
  [8,5,2],
  [9,6,3]
]

Example 2:

Given input matrix =
[
  [ 5, 1, 9,11],
  [ 2, 4, 8,10],
  [13, 3, 6, 7],
  [15,14,12,16]
], 

rotate the input matrix in-place such that it becomes:
[
  [15,13, 2, 5],
  [14, 3, 4, 1],
  [12, 6, 8, 9],
  [16, 7,10,11]
]

wrong code:

class Solution {
    public void rotate(int[][] matrix) {
        int n = matrix.length;
        for(int i = 0; i < n ; i++){
            rotateOneLayer(matrix,0,n-1);
        }
    }
    
    public void rotateOneLayer(int[][] matrix, int start, int end){
        for(int i = 0; i < end; i++){
            int temp = matrix[start][start+i];
            matrix[start][start+i] = matrix[end-i][start];
            matrix[end-i][start] = matrix[end][start+i];
            matrix[end][start+i] = matrix[start+i][end];
            matrix[start+i][end] = temp;
        }
    }
}

correct code:

class Solution {
    public void rotate(int[][] matrix) {

        int n = matrix.length;
        int lc = 0;
        int lr = 0;
        int rc = n - 1;
        int rr = n - 1;
        while(lr < rr){
            rotateOneLayer(matrix,lr, lc, rr, rc);
            lr++;
            lc++;
            rr--;
            rc--;
        }
    }
    
    public void rotateOneLayer(int[][] matrix, int lr, int lc, int rr, int rc){
        
        int times = rr - lr;
        if(lr == rr) return;
        for(int i = 0; i < times; i++){
            int temp = matrix[lr][lc+i];
            matrix[lr][lc+i] = matrix[rr-i][lc];//从上面往上算
            matrix[rr-i][lc] = matrix[rr][rc-i];//从最左节点往前算
            matrix[rr][rc-i] = matrix[lc+i][rc];
            matrix[lc+i][rc] = temp;
        }
    }
}