19.2.7 [LeetCode 48] Rotate Image

Posted 2021-02-08 TobicYAL

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]
]

题意

在没有额外空间的前提下90度顺时针旋转n*n矩阵

题解

日常暴力↓

 1 class Solution {
 2 public:
 3     void rotate(vector<vector<int>>& matrix) {
 4         int n = matrix.size(), layer = n / 2;
 5         for (int i = 0; i < layer; i++) {
 6             for (int j = i; j < n - 1 - i; j++) {
 7                 int now = matrix[i][j];
 8                 matrix[i][j] = matrix[n - 1 - j][i];
 9                 matrix[n - 1 - j][i] = matrix[n - 1 - i][n - 1 - j];
10                 matrix[n - 1 - i][n - 1 - j] = matrix[j][n - 1 - i];
11                 matrix[j][n - 1 - i] = now;
12             }
13         }
14     }
15 };

View Code

但是问题是也找不到更快的解法,逐渐怀疑是不是今天系统的问题....beat 2%也太夸张了,大家都是咋做的啊