算法作業_28(2017.6.8第十六週)

64. 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

解析:還是一到動態規劃,矩陣dp第一行和第一列需要單獨處理:

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


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