Leetcode 120: 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.

 

public class Solution {
    public int MinimumTotal(IList<IList<int>> triangle) {
        int count = triangle.Count;
        
        if (count == 0) return 0;
        
        var dp = new int[count + 1];
        
        for (int i = count - 1; i >= 0; i--)
        {
            for (int j = 0; j < triangle[i].Count; j++)
            {
                dp[j] = triangle[i][j] + Math.Min(dp[j], dp[j + 1]);
            }
        }
        
        return dp[0];        
    }
}