048.md

Rotate Image

题目

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.

example1:
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]
]

example2:
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]
]

思路

按照对角线对称交换 即matrix[i][j] = matrix[j][i]

再对每一行进行处理，按照中间线，对称交换 即 matrix[i][j] = matrix[i][sz-j-1]//sz为一行的长度

代码

class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        int sz = matrix.size();
        //对角线转换
        for(int i=0;i<sz;++i){
            for(int j=i+1;j<sz;++j){
                swap(matrix[i][j],matrix[j][i]);
            }
        }
        //中间轴 对称交换
        for(int i=0;i<sz;++i){
            for(int j=0;j<sz/2;++j){
                swap(matrix[i][j],matrix[i][sz-j-1]);
            }
        }
        
    }
};