LeetCode 59. Spiral Matrix II（递归）

题目来源：https://leetcode.com/problems/spiral-matrix-ii/

问题描述

59. Spiral Matrix II

Medium

Given a positive integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

Example:

Input: 3

Output:

[

 [ 1, 2, 3 ],

 [ 8, 9, 4 ],

 [ 7, 6, 5 ]

]

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题意

给出正整数n，返回n×n的矩阵，其中元素为1~n*n的顺时针从外向里螺旋排列

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思路

递归。首先填充外圈，然后递归调用填充内部矩形。

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代码

class Solution {
    private void recuFill(int[][] mat, int x, int m, int cnt)
    {
        if (m == 0)
        {
            return;
        }
        else if (m == 1)
        {
            mat[x][x] = cnt;
            return;
        }
        int i = 0;
        for (i=x; ix; i--)
        {
            mat[x+m-1][i] = cnt++;
        }
        for (i=x+m-1; i>x; i--)
        {
            mat[i][x] = cnt++;
        }
        recuFill(mat, x+1, m-2, cnt);
    }    

    public int[][] generateMatrix(int n) {
        int[][] ret = new int[n][n];
        recuFill(ret, 0, n, 1);
        return ret;
    }
}