48.Rotate Image

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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]
]

我的解法

解题思路

其实把要转换的次数以及每次转换对应的位置找到规律就可以了

实现代码

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class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        
        int n = matrix.size();
        for (int i = 0; i < n / 2; i++){
            for (int j = i; j < n - i - 1; j++){
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[n-j-1][i];
                matrix[n-j-1][i] = matrix[n-i-1][n-j-1];
                matrix[n-i-1][n-j-1] = matrix[j][n-i-1];
                matrix[j][n-i-1] = tmp;
            }
        }
    }
};

Runtime: 0 ms, faster than 100.00% of C++ online submissions for Rotate Image.
Memory Usage: 9 MB, less than 87.81% of C++ online submissions for Rotate Image.

也可以先上线翻转，再对角线翻转：

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class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        int n = matrix.size();
        if (n == 0) return;
        for (int i = 0; i < n / 2; i++){
            for (int j = 0; j < n; j++){
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[n-i-1][j];
                matrix[n-i-1][j] = tmp;
            }
        }
        for (int i = 0; i < n; i++){
            for (int j = i; j < n; j++){
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = tmp;
            }
        }
    }
};