Rotate Image

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问题描述

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

Rotate the image by 90 degrees (clockwise).

For example:
Input:　　[[1, 2], [3, 4]]
Output: [[3, 1], [4, 2]];

思考：怎么变换使用O（1）的空间

想法：先对矩阵进行对角线变换，然后对每一行，进行逆序变换

public class Solution {    public void rotate(int[][] matrix) {        diagSwap(matrix);        rowReverse(matrix);    }    private void diagSwap(int[][] matrix){        if (matrix.length < 2)            return;        for(int i = 0; i < matrix.length; i++)            for(int j = 0; j < i; j++)                swap(i, j, j, i, matrix);    }    private void swap(int oR, int oC, int Tr, int Tc, int[][] matrix){        int temp = matrix[oR][oC];        matrix[oR][oC] = matrix[Tr][Tc];        matrix[Tr][Tc] = temp;    }    private void rowReverse(int[][] matrix){        if(matrix.length == 0 )            return ;              int len = matrix[0].length;        for(int i = 0; i < matrix.length; i++)            for(int j = 0; j < (len >> 1); j++)                swap(i, j, i, len - j - 1, matrix);    }}

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