class Solution {
public:
    int minPathSum(vector<vector<int>>& grid) {
        int m = grid.size(), n = grid[0].size();
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                // 边界只有一种走法  
                if (i == 0) {
                    if (j > 0) grid[i][j] += grid[i][j - 1];
                } 
                else if (j == 0) {
                    if (i > 0) grid[i][j] += grid[i - 1][j];
                }
                // 内部取最小值走
                else {
                    grid[i][j] += min(grid[i - 1][j], grid[i][j - 1]);
                }
            }
        }
        return grid[m - 1][n - 1];
    }
};

class Solution {
public:
    string minWindow(string s, string t) {
        vector<int> worker(128, 0);
        for (char &c : t) ++worker[c];
        int l = 0, r = 0, n = t.size(), len = INT_MAX, start = 0;
        while (r < s.size()) {
            // 非t类字母永远 >= 0
            if (worker[s[r++]]-- > 0) --n; 
            while (!n) {
                if (r - l < len) len = r - (start = l);
                // t类字母永远 <= 0
                if (++worker[s[l++]] > 0) ++n;
            }
        }
        return len == INT_MAX ? "" : s.substr(start, len);
    }
};