59. Spiral Matrix II

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 ]]

题意就是做一个n*n的回环。

我的思路是定义x，y记录位置，index记录数值。一圈一圈向内填充。最外层循环4次 每次循环n-1次，最后x=0，y=0。x++，y++后进入更内一层，4*(n-3)的循环，以此类推。

class Solution {    public int[][] generateMatrix(int n) {        int num[][] = new int[n][n];        int x = 0;        int y = 0;        int index = 1;        for(int i = 1;i<=n/2;i++){            for(int j = 0;j<n+1-i*2;j++){                num[x][y] = index;                index++;                y++;            }            for(int j = 0;j<n+1-i*2;j++){                num[x][y] = index;                index++;                x++;            }            for(int j = 0;j<n+1-i*2;j++){                num[x][y] = index;                index++;                y--;            }            for(int j = 0;j<n+1-i*2;j++){                num[x][y] = index;                index++;                x--;            }            x++;            y++;        }        if(n%2 == 1)            num[n/2][n/2] = n*n;        return num;    }}