LeetCode 94 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 ]
]分析：
一圈一圈从外向里赋值。

维持一个layer变量，这样就可以每一圈分开处理。

public class Solution {
public int[][] generateMatrix(int n) {
int[][] res = new int

;
int length=n;
int val = 1;
//一层一层往里赋值
for(int layer=0; layer<n/2; layer++){
for(int col=layer; col<layer+length; col++){//顶
res[layer][col] = val++;
}
for(int row=layer+1; row<layer+length; row++){//右
res[row][layer+length-1] = val++;
}
for(int col=layer+length-2; col>=layer; col--){//下
res[layer+length-1][col] = val++;
}
for(int row=layer+length-2; row>layer; row--){//左
res[row][layer] = val++;
}
length -= 2;//宽度每次减2
}
if(n%2 != 0)//奇数中间的一个数字还没有处理
res[n/2][n/2] = val;
return res;
}
}