[Leetcode] Rotate Image

Rotate Image 题解

题目来源：https://leetcode.com/problems/rotate-image/description/

---

Description

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

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]
]

Solution

class Solution {
public:
    void rotate(vector<vector<int> >& matrix) {
        int n = matrix.size();
        reverse(matrix.begin(), matrix.end());
        int i, j;
        for (i = 0; i < n; i++) {
            for (j = i; j < n; j++)
                swap(matrix[i][j], matrix[j][i]);
        }
    }
};

---

解题描述

这道题题意是，给出一个正方形的矩阵代表一副图像，求将图像顺时针旋转之后的矩阵，并且要求原地旋转，不能申请新的矩阵。上面用到的解法是，先将矩阵进行上下翻转，然后再进行对角线上的翻转即可。