Dynamic Programming: Suppose we have a m by n matrix filled with non-negative integers, find a pah from top left corner to bottom right corner which minimizes the sum of all numbers along its path in Python

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.