leetcode JAVA Spiral Matrix II 难度系数3 3.19

Question：

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[][] result = new int

;
if (n < 1)
return result;
int top = 0, bottom = n - 1, left = 0, right = n - 1;
int loop = (n + 1) / 2;
for (int i = 0, num = 1; i < loop; i++) {
for (int j = left; j <= right; j++) {
result[top][j] = num++;
}
top++;
if (top > bottom)
return result;
for (int j = top; j <= bottom; j++) {
result[j][right] = num++;
}
right--;
if (left > right)
return result;
for (int j = right; j >= left; j--) {
result[bottom][j] = num++;
}
bottom--;
if(top>bottom) return result;
for(int j=bottom;j>=top;j--){
result[j][left]=num++;
}
left++;
}
return result;
}
}