[LintCode] 螺旋矩阵II Spiral Matrix II

Given an integer n, generate a square matrix filled with elements from 1 to n^2 in spiral order.

样例

Given n = 3,

You should return the following matrix:

[

[ 1, 2, 3 ],

[ 8, 9, 4 ],

[ 7, 6, 5 ]

]

public class Solution {
/**
* @param n an integer
* @return a square matrix
*/
public int[][] generateMatrix(int n) {
if(n < 0) return null;
int[][] matrix = new int

;
if(n == 0) return matrix;
int circle = 0, num = 1;
while(circle <= (n-1)/2) {
int i = circle, j = circle;
matrix[i][j] = num++;
while(j < n-i-1) {
matrix[i][++j] = num++;
}
while(i < j) {
matrix[++i][j] = num++;
}
while(j > n-i-1) {
matrix[i][--j] = num++;
}
while(i > j+1) {
matrix[--i][j] = num++;
}
circle++;
}
return matrix;
}
}