leetcode 10: 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, wheren is the total number of rows in the triangle.

 

 

class Solution {
public:
    int minimumTotal(vector<vector<int> > &triangle) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int n = triangle.size();
        
        vector<int> rel( triangle[n-1] );
        for( int i= n-2; i >= 0 ; --i) {
            for( int j = 0; j<triangle[i].size(); ++j) {
                rel[j] = triangle[i][j] + min( rel[j], rel[j+1] );
            }
        }
        
        return rel[0];
    }
};