luzhipeng aea6437 May 29, 2019
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## 题目地址

https://leetcode.com/problems/rotate-image/description/

## 题目描述

``````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]
]

``````

## 思路

```var rotate = function(matrix) {
// 时间复杂度O(n^2) 空间复杂度O(n)
const oMatrix = JSON.parse(JSON.stringify(matrix)); // clone
const n = oMatrix.length;
for (let i = 0; i < n; i++) {
for (let j = 0; j < n; j++) {
matrix[j][n - i - 1] = oMatrix[i][j];
}
}
};```

• 矩阵旋转操作

## 代码

```/*
* @lc app=leetcode id=48 lang=javascript
*
* [48] Rotate Image
*/
/**
* @param {number[][]} matrix
* @return {void} Do not return anything, modify matrix in-place instead.
*/
var rotate = function(matrix) {
// 时间复杂度O(n^2) 空间复杂度O(1)

// 做法： 先沿着对角线翻转，然后沿着水平线翻转
const n = matrix.length;
function swap(arr, [i, j], [m, n]) {
const temp = arr[i][j];
arr[i][j] = arr[m][n];
arr[m][n] = temp;
}
for (let i = 0; i < n - 1; i++) {
for (let j = 0; j < n - i; j++) {
swap(matrix, [i, j], [n - j - 1, n - i - 1]);
}
}

for (let i = 0; i < n / 2; i++) {
for (let j = 0; j < n; j++) {
swap(matrix, [i, j], [n - i - 1, j]);
}
}
};```
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