LeetCode-48-Rotate Image

Rotate Image

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来自 <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?

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题目解读

给定一个n?x?n的2D矩阵代表一张图片，将图片旋转90度（顺时针方向）。

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你能在原地解决吗？

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解析：将二维矩阵先第0行与第n-1行、第1行与第n-2行…进行交换，然后按照主对角线进行交换。可得到旋转90°的效果

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Java代码

public class Solution {
    public void rotate(int[][] matrix) {
        int low = 0;
		int high = matrix.length-1;
		int temp = 0;
		//第一次进行上下交换
		while(low<high) {
			for(int i=0; i<matrix.length; i++){
				temp = matrix[low][i];
				matrix[low][i] = matrix[high][i];
				matrix[high][i] = temp;
			}
			low++;
			high--;
		}
		
		//第二次按照主对角线进行交换
		for(int i=0; i< matrix.length; i++) {
			for(int j=i; j<matrix.length; j++) {
				temp = matrix[i][j];
				matrix[i][j] = matrix[j][i];
				matrix[j][i] = temp;
			}
		}
    }
}

代码性能

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LeetCode-48-Rotate Image

原文：http://972459637-qq-com.iteye.com/blog/2241480