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 ]
]

此題跟之前那道本質上沒什麽區別，就相當於個類似逆運算的過程，這道題是要按螺旋的順序來填數，由於給定矩形是個正方形，我們計算環數時用n / 2來計算，若n為奇數時，註意一下中間點。

class Solution {
public:
    vector<vector<int>> generateMatrix(int n) {
         
        vector<vector<int>> v(n,vector<int>(n,1));
        int cnt = 1;
        int p=n; 
        for (int i=0; i<n/2; i++, p=p-2){
            for(int col=i; col < i+p; col ++){
                v[i][col] 
 
= cnt++;
            }
            for(int row=i+1; row < i+p; row++){
                v[row][i+p-1] = cnt++;
            }
            for(int col=i+p-2; col>=i; col--){
                v[i+p-1][col] = cnt++;
            }
            for(int row=i+p-2; row>i; row--){
                v[row][i] 
 
= cnt++;
            }
            
        }
        if((n%2) == 1)v[n/2][n/2] = cnt;
        return v;
    }
};

LeetCode 59 Spiral Matrix II 螺旋矩陣之二