LeetCode Spiral Matrix II (生成螺旋矩阵)



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 ]
]

题意：给出矩阵的维数，将1-n^2的数填入螺旋矩阵中

思路：与LeetCode Spiral Matrix(螺旋矩阵)方法类似，只是一个逆过程而已

代码如下

public class Solution {
    public int[][] generateMatrix(int n) {
        int[][] matrix = new int[n][n];

        int[][] dir = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};

        boolean[][] vis = new boolean[n][n];

        int cnt = 0;
        int total = n * n;
        int cur = 0;
        int x = 0, y = 0;
        int nextx = 0, nexty = 0;

        while (cnt < total)
        {
            if (!vis[x][y])
            {
                matrix[x][y] = cnt + 1;
                vis[x][y] = true;
                cnt++;
            }

            nextx = x + dir[cur][0]; nexty = y + dir[cur][1];

            if (nextx < 0 || nextx >= n || nexty < 0 || nexty >= n || vis[nextx][nexty] == true)
            {
                cur = (cur + 1) % 4;
                continue;
            }

            x = nextx; y = nexty;
        }

        return matrix;
    }
}