64. Minimum Path Sum

https://leetcode.com/problems/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.

Example:

Input: [ [1,3,1], [1,5,1], [4,2,1] ] Output: 7

Explanation: Because the path 1→3→1→1→1 minimizes the sum.