Spiral Matrix II

Given an integer n, generate a square matrix filled with elements from 1 ton2 in spiral order.

For example,
Given n = 3,

You should return the following matrix:

[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]

思路：这个算法跟之前的 Sprial Matrix I，一模一样。

class Solution {
    public int[][] generateMatrix(int n) {
        int startX = 0; int endX = n - 1;
        int startY = 0; int endY = n - 1;
        int[][] res = new int[n][n];
        
        int value = 1;
        while(startX <= endX && startY <= endY) {
            // top;
            for(int j = startY; j <= endY; j++) {
                res[startX][j] = value++;
            }
            if(++startX > endX) break;
            
            // right;
            for(int i = startX; i <= endX; i++) {
                res[i][endY] = value++;
            }
            if(--endY < startY) break;
            
            // bottom;
            for(int j = endY; j >= startY; j--) {
                res[endX][j] = value++;
            }
            if(--endX < startX) break;
            
            // left;
            for(int i = endX; i >= startX; i--) {
                res[i][startY] = value++;
            }
            if(++startY > endY) break;
        }
        return res;
    }
}