Spiral MatrixII.txt

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 ]
]

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 vector<vector<int> > generateMatrix(int n)
 {
	vector<vector<int> > matrix(n, vector<int>(n));
	if(n == 0)
		return matrix;
	int left = 0, right = n - 1;
	int up = 0, down = n - 1;
	int num = 1;
	while(true)
	{
		//from left to right
		for(int i = left; i <= right; ++i)
			matrix[left][i] = num++;
		if(++up > down)return matrix;

		//from up to down
		for(int i = up; i <= down; ++i)
			matrix[i][right] = num++;
		if(left > -- right)return matrix;

		//from right to left
		for(int i = right; i >= left; --i)
			matrix[down][i] = num++;
		if(up > -- down)return matrix;

		//from down to up
		for(int i = down; i >= up; --i)
			matrix[i][left] = num++;
			if(++left > right)return matrix;
	}
 }