64. Minimum Path Sum Medium

求到达右下角的路径，使得路径上数的和最小。比较简单。每一个位置你选择从上面来更小还是左边来更小就好。

class Solution {public:    int minPathSum(vector<vector<int>>& grid) {        int m = grid.size(), n = grid[0].size();        int d[m][n];        for (int i = 0; i < m; ++i)        {        for (int j = 0; j < n; ++j)        {        if(i == 0 && j == 0)d[i][j] = grid[0][0];        else if (i == 0 && j != 0)        {        d[i][j] = d[i][j - 1] + grid[i][j];        }        else if (j == 0 && i != 0)        {        d[i][j] = d[i - 1][j] + grid[i][j];        }        else {        d[i][j] = min(d[i - 1][j], d[i][j - 1]) + grid[i][j];        }        }        }        return d[m - 1][n - 1];    }};