48. Rotate Image

source: https://leetcode.com/problems/rotate-image/

Question

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.

思路

顺时针旋转形象点想的话，就是去把原本矩阵的每行给立起来。

/**
 * @param {number[][]} matrix
 * @return {void} Do not return anything, modify matrix in-place instead.
 */
var rotate = function (matrix) {
    const n = matrix.length;
    const ret = [];
    for (let x = 0; x < n; x++) ret.push([]);
    for (let y = n - 1; y >= 0; y--) {
        const line = matrix[y];
        for (let x = 0; x < n; x++) {
            ret[x][n - 1 - y] = line[x];
        }
    }
    for (let x = 0; x < n; x++) matrix[x] = ret[x];
};

总结

对于这种题目要先多观察，总结规律然后开始写题，事半功倍。