Rotate Image
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?
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)。
你能在原地解决吗?
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
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