leetcode - Spiral Matrix II

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,

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

class Solution {
public:
    std::vector > generateMatrix(int n) {
		std::vector> matrix(n,std::vector(n,0));
		int start = 0, end = n - 1;
		int step = 1;
		while(start < end)
		{
			for (int i = start; i < end; i++)
			{
				matrix[start][i] = step++;
			}
			for (int i = start; i < end; i++)
			{
				matrix[i][end] = step++;
			}
			for(int i = end; i > start; i--)
			{
				matrix[end][i] = step++;
			}
			for(int i = end; i > start; i--)
			{
				matrix[i][start] = step++;
			}
			start++;
			end--;
		}
		if(start == end)
		{
			matrix[start][end] = step++;
		}
		return matrix;
    }
};