Rotate Image

問題描述

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：怎麼變換使用O（1）的空間

想法：先對矩陣進行對角線變換，然後對每一行，進行逆序變換

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);
    }
}