[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.

 

分析：动态规划。f[i][j] = min(f[i-1][j], f[i][j-1]) + a[i][j]

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