LeetCode每日一题：spiral matrix ii

问题描述

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.
For example,
Given n =3,
You should return the following matrix:
[
[ 1, 2, 3 ],
[ 8, 9, 4 ],
[ 7, 6, 5 ]
]

问题分析

和上题类似，只需要按照便利顺序一层层地添加就好了。

代码实现

public int[][] generateMatrix(int n) {
        int[][] res = new int[n][n];
        int left = 0, right = n - 1, bottom = n - 1, top = 0, num = 1;
        while (left < right && top < bottom) {
            for (int i = left; i < right; i++) {
                res[top][i] = num++;
            }
            for (int i = top; i < bottom; i++) {
                res[i][right] = num++;
            }
            for (int i = right; i > left; i--) {
                res[bottom][i] = num++;
            }
            for (int i = bottom; i > top; i--) {
                res[i][left] = num++;
            }
            top++;
            bottom--;
            left++;
            right--;
        }
        if (n % 2 == 1) {
            res[n / 2][n / 2] = num;
        }
        return res;
    }