Leetcode120-triangle

Description

Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.

For example, given the following triangle

[
     [2],
    [3,4],
   [6,5,7],
  [4,1,8,3]
]

The minimum path sum from top to bottom is 11 (i.e., 2 + 3 + 5 + 1 = 11).

Note:

Bonus point if you are able to do this using only O(n) extra space, where n is the total number of rows in the triangle.

Solution

class Solution {
    public int minimumTotal(List<List<Integer>> triangle) {
        int[] dp = new int[triangle.size() + 1];
        for (int i = triangle.size() - 1; i >= 0; i--){
            for (int j = 0; j <= i; j++){
                dp[j] = Math.min(dp[j], dp[j + 1]) + triangle.get(i).get(j); 
            }
        }
        return dp[0];
    }
}

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