leetcode- 48. Rotate Image

一、问题描述

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]
]

二、代码

class Solution {
public:
    void rotate(vector > &matrix) {
        if (matrix.empty()) 
            return;
        int n = matrix.size();

        for (int layer = 0; layer < n / 2; layer++) {
             for (int i = layer; i < n - layer - 1; i++) {
                 int temp = matrix[layer][i];
                 matrix[layer][i] = matrix[n-1-i][layer];
                 matrix[n-1-i][layer] = matrix[n-1-layer][n-1-i];
                 matrix[n-1-layer][n-1-i] = matrix[i][n-1-layer];
                 matrix[i][n-1-layer] = temp;
             }
        }
    }
};