Spiral Matrix II

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> > matrix(n, vector<int>(n,0));//result
        int dec = 0;//decrement count
        int row = 0;//start row
        int col = 0;//start col
        int lastIndex = 0;
        int const n2 = n*n;
        int counter = 1;
        while(1){
            lastIndex = n-1 -dec + col;
            for(int ii = col; ii <= lastIndex; ++ii){//left to right
                matrix[row][ii] = counter++;
            }
            col = lastIndex;
            ++row;
            ++dec;
            if (counter > n2) return matrix;
            
            lastIndex = n-1 -dec + row;
            for(int ii = row; ii <= lastIndex; ++ii){//up to down
                matrix[ii][col] = counter++;
            }
            row = lastIndex;
            --col;
            if (counter > n2) return matrix;
            
            lastIndex = col - (n-1-dec);
            for(int ii = col; ii >= lastIndex; --ii){//right to left
                matrix[row][ii] = counter++;
            }
            col = lastIndex;
            --row;
            ++dec;
            if (counter > n2) return matrix;
            
            lastIndex = dec + row + 1 - n;
            for(int ii = row; ii >= lastIndex; --ii){//down to up
                matrix[ii][col] = counter++;
            }
            row = lastIndex;
            ++col;
            if (counter > n2) return matrix;
        }
        return matrix;
    }
};