[leetcode] Rotate Image

Cabinathor

于 2015-06-20 16:10:46 发布

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本文链接：https://blog.youkuaiyun.com/lmxmimihuhu/article/details/46574071

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本文介绍了如何在原地旋转给定的二维矩阵90度，包括代码实现和原理解释。

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

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up:
Could you do this in-place?

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

public class Solution {
    public void rotate(int[][] matrix) {
        if(null == matrix || null == matrix[0]) {
            return;
        }
        int n = matrix.length;
        if(n <= 1 || matrix[0].length != n) {
            return;
        }
        for(int i=0, N=n-1; i<(n>>1); ++i) {
            for(int j=i; j<N-i; ++j) {
                int t = matrix[i][j];
                matrix[i][j] = matrix[N-j][i];
                matrix[N-j][i] = matrix[N-i][N-j];
                matrix[N-i][N-j] = matrix[j][N-i];
                matrix[j][N-i] = t;
            }
        }
    }
}