64. Minimum Path Sum

Given amxngrid filled with non-negative numbers, find a path from top left to bottom right whichminimizesthe sum of all numbers along its path.

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

第一种方法m*n 空间复杂度 

第二种方法 m空间复杂度

DP formula  dp[i+1] = min(dp[i+1], dp[i]) +value[i][j];