59. Spiral Matrix II

---

Given a positive integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

Example:

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

class Solution {
public:
    vector<vector<int>> generateMatrix(int n) {
        vector<vector<int> > res( n, vector<int>(n) );
        int n1 =1;
        int c1=0,c2=n-1;
        int r1=0,r2=n-1;
        while(c1<=c2&&r1<=r2){
            for(int c =c1;c<=c2;c++,n1++) res[r1][c] =n1;
            for(int r =r1+1;r<=r2;r++,n1++) res[r][c2] =n1;
            if(c1<=c2&&r1<=r2){
            for(int c =c2-1;c>=c1;c--,n1++) res[r2][c] =n1;
            for(int r =r2-1;r>=r1+1;r--,n1++) res[r][c1] =n1;
            }
            c1++;c2--;r1++;r2--;
        }
        return res;
    }

};