LeetCode_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 ]
]

　　

class Solution {
public:
    vector<vector<int> > generateMatrix(int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<vector<int>> res(n,vector<int>(n));
        
        int lays = (n+1)/2;
        bool single = n%2;
        int num = 1;
        for(int lay = 0; lay < lays; lay ++){
        
            int topRow = lay;
            int rightColumn = n - 1 - lay;
            
            //process the top
            for(int i = lay; i <= rightColumn; i++)
                  res[topRow][i] = num++;
                  
            //process the right Column
            for(int i = lay+1; i <= rightColumn ;i++)
                  res[i][rightColumn] = num++;
                  
            if(lay == lays -1 && single )
                    continue;
                    
            //process the bottom 
            for(int i = rightColumn - 1; i>= lay; i--)
                  res[rightColumn][i] = num++;
                  
            for(int i = rightColumn - 1; i> lay ;i--)
                 res[i][lay] = num++;
        
        }
        
        return res;
    }
};