寻找矩阵中最短路径 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.

算法：动态规划法，因为只能向下或者右行走，所以从[1,1]位置开始，当前最小路径由上方与左方即[0,1],[1,0]最小值决定。

代码

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

        for (int k = 1; k < m; ++k) {
            for (int l = 1; l < n; ++l) {
                grid[k][l] = min(grid[k-1][l],grid[k][l-1]) + grid[k][l];
            }
        }
        return grid[m-1][n-1];
    }
};