Blogs Hub

by Sumit Chourasia | Nov 17, 2020 | Category :coding | Tags : algorithm array data-structure leetcode medium

Triangle - Array - Medium - LeetCode

Triangle - Array - Medium - LeetCode

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 rows = triangle.Count();
        
        for(int i=1;i<rows;i++){
            for(int j=0;j<triangle[i].Count();j++){
                if(j==0 || j == triangle[i].Count()-1){
                    if(j > triangle[i-1].Count()-1){
                        triangle[i][j]+=triangle[i-1][j-1];
                    }
                    else{
                        triangle[i][j]+=triangle[i-1][j];
                    }                    
                }
                else{
                    triangle[i][j] += Math.Min(triangle[i-1][j-1], triangle[i-1][j]);
                }
            }
                        
        }
        
        int min = int.MaxValue;
        
        for(int i=0;i<triangle[rows-1].Count();i++){
            min = Math.Min(min, triangle[rows-1][i]);
        }
        
        return min;
    }        
}

Time Complexity: O(m*n)

Space Complexity: O(1)