leetcode解题方案--048--Rotate Image

题目

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.

分析

旋转操作很简单，找到规律就可以啦。
别的。。。突然发现题目中不让申请其他数组空间。而我的思路是dfs。就是利用dfs进行遍历，申请了marked数组来标记已经旋转过的位置，应该是不对的。

另外就是用数学方法计算到底怎样才能不多旋转，也非常简单。按框框来算，每一个框框只需要旋转（n-1）*4次就可以啦

class Solution {    public static void rotate(int[][] xx) {        int n = xx.length;        boolean[][] marked = new boolean[n][n];        for (int i = 0; i < n; i++) {            for (int j = 0; j < n; j++) {                if (marked[i][j] == true) {                    continue;                }                int newValue = xx[i][j];                dfs(xx, j, n -1 - i, newValue, marked);            }        }    }    public static void dfs(int[][] xx, int x, int y, int value, boolean[][] marked) {        int newValue = xx[x][y];        xx[x][y] = value;        marked[x][y] = true;        if (!marked[y][xx.length - 1-x]) {            dfs(xx, y, xx.length - x-1, newValue, marked);        }    }}