[LeetCode] Minimum Path Sum

Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path.

Note: You can only move either down or right at any point in time.

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