leetcode Spiral Matrix

题目连接

https://leetcode.com/problems/spiral-matrix/ 

Spiral Matrix

Description

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

For example, 
Given the following matrix:

[ 
　　[ 1, 2, 3 ], 
　　[ 4, 5, 6 ], 
　　[ 7, 8, 9 ] 
] 
You should return [1,2,3,6,9,8,7,4,5].

蛇形填数。。

class Solution {
public:
	vector<int> spiralOrder(vector<vector<int>>& matrix) {
		ans.clear();
		if (matrix.empty() || matrix[0].empty()) return ans;
		n = matrix.size(), m = matrix[0].size();
		int x = 0, y = 0, tot = 1;
		vector<vector<int>> vis(n, vector<int>(m));
		ans.push_back(matrix[x][y]), vis[x][y] = true;
		while (tot < n * m) {
			while (y + 1 < m  && !vis[x][y + 1]) ans.push_back(matrix[x][++y]), vis[x][y] = true, tot++;
			while (x + 1 < n  && !vis[x + 1][y]) ans.push_back(matrix[++x][y]), vis[x][y] = true, tot++;
			while (y - 1 >= 0 && !vis[x][y - 1]) ans.push_back(matrix[x][--y]), vis[x][y] = true, tot++;
			while (x - 1 >= 0 && !vis[x - 1][y]) ans.push_back(matrix[--x][y]), vis[x][y] = true, tot++;
		}
		return ans;
	}
private:
	int n, m;
	vector<int> ans;
};