Leetcode 48 旋转图像(Rotate Image) 题解分析

You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).

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.

如图，这道题以前做过，其实一看有点蒙，好像规则很容易描述，但是代码很难写，因为要类似于贪吃蛇那样，后来想着应该会有一些特殊的技巧，比如翻转等

public void rotate(int[][] matrix) {
        // 这里真的傻了，长宽应该是一致的，所以取一次就够了
        int lengthX = matrix[0].length;
        int lengthY = matrix.length;
        int temp;
        System.out.println(lengthY - (lengthY % 2) / 2);
        // 这里除错了，应该是减掉余数再除 2
//        for (int i = 0; i < lengthY - (lengthY % 2) / 2; i++) {
        /**
         * 1 2 3             7 8 9
         * 4 5 6     =>      4 5 6     先沿着 4 5 6 上下交换
         * 7 8 9             1 2 3
         */
        for (int i = 0; i < (lengthY - (lengthY % 2)) / 2; i++) {
            for (int j = 0; j < lengthX; j++) {
                temp = matrix[i][j];
                matrix[i][j] = matrix[lengthY-i-1][j];
                matrix[lengthY-i-1][j] = temp;
            }
        }

        /**
         * 7 8 9               7 4 1
         * 4 5 6     =>        8 5 2   这里再沿着 7 5 3 这条对角线交换
         * 1 2 3               9 6 3
         */
        for (int i = 0; i < lengthX; i++) {
            for (int j = 0; j <= i; j++) {
                if (i == j) {
                    continue;
                }
                temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
            }
        }
    }

还没到可以直接归纳题目类型的水平，主要是几年前做过，可能有那么点模糊的记忆，当然应该也有直接转的方法