leetcode Spiral Matrix

原題鏈接：https://leetcode.com/problems/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].
蛇形填數。。

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;
};