Triangle

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:

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