[Solved] 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.

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Question

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 1:

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Input: grid = [[1,3,1],[1,5,1],[4,2,1]]
Output: 7
Explanation: Because the path 1 → 3 → 1 → 1 → 1 minimizes the sum.

Example 2:

Input: grid = [[1,2,3],[4,5,6]]
Output: 12

Constraints:

  • m == grid.length
  • n == grid[i].length
  • 1 <= m, n <= 200
  • 0 <= grid[i][j] <= 100

Python Solution

class Solution:
    def minPathSum(self, grid: List[List[int]]) -> int:
        m = len(grid[0])
        n = len(grid)

        for i in range (1,n):
            grid[i][0] = grid[i][0] + grid[i-1][0]

        for i in range(1,m):
            grid[0][i] = grid[0][i] + grid[0][i-1]

        for i in range (1,n):
            for j in range (1,m):
                grid[i][j] = min(grid[i][j] + grid[i-1][j] , grid[i][j] + grid[i][j-1])

        return grid[-1][-1]

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