LeetCode - Triangle

Given a triangle array, return the minimum path sum from top to bottom.

For each step, you may move to an adjacent number of the row below. More formally, if you are on index i on the current row, you may move to either index i or index i + 1 on the next row.

 

Example 1:

Input: triangle = [[2],[3,4],[6,5,7],[4,1,8,3]]
Output: 11
Explanation: The triangle looks like:
   2
  3 4
 6 5 7
4 1 8 3
The minimum path sum from top to bottom is 2 + 3 + 5 + 1 = 11 (underlined above).

Example 2:

Input: triangle = [[-10]]
Output: -10

 

Constraints:

• 1 <= triangle.length <= 200
• triangle[0].length == 1
• triangle[i].length == triangle[i - 1].length + 1
• -104 <= triangle[i][j] <= 104

 

ChatGPT's Solution:

class Solution:
    def minimumTotal(self, triangle: List[List[int]]) -> int:
        # Start from the second-last row and go upward
        for row in range(len(triangle) - 2, -1, -1):
            for col in range(len(triangle[row])):
                # Update the current cell to include the min path sum below it
                triangle[row][col] += min(triangle[row + 1][col], triangle[row + 1][col + 1])
        
        # The top element now contains the minimum path sum
        return triangle[0][0]