[leetCode] 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 ]]

public class Solution {    public int[][] generateMatrix(int n) {        int[][] res = new int[n][n];        int x0 = 0, x1 = n - 1, y0 = 0, y1 = n - 1;        int ele = 0;        while (x0 <= x1 && y0 <= y1) {            for (int i = y0; i <= y1; i++) {                res[x0][i] = ++ele;            }            for (int i = x0 +1; i <= x1; i++) {                res[i][y1] = ++ele;            }            if (x0 == x1) break;            for (int i = y1 - 1; i >= y0; i--) {                res[x1][i] = ++ele;            }            if (y0 == y1) break;            for (int i = x1 - 1; i > x0; i--) {                res[i][y0] = ++ele;            }            x0++; x1--; y0++; y1--;        }        return res;    }}