[Leetcode] triangle

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 is11(I. e., 2 + 3 + 5 + 1 = 11 ).

Note:
Bonus Point if you are able to do this using onlyO(N) Extra space, whereNIs the total number of rows in the triangle.

Algorithm ideas:

Thought 1:

From top to bottom, use an array to record the weighted situation of all nodes from the root node to the I layer. When you fall to the last layer, you can find the shortest path. Requires O (n) space.

Not Implemented

 

Idea 2:

 1     public int minimumTotal(List<List<Integer>> triangle) { 2         if(triangle == null || triangle.size() == 0) return 0; 3         int height = triangle.size(); 4         for(int i = height - 2; i >= 0; i--){ 5             List<Integer> list = triangle.get(i); 6             for(int j = 0; j < list.size();j++){ 7                 int min = triangle.get(i + 1).get(j) < triangle.get(i + 1).get(j + 1) ? triangle.get(i + 1).get(j) : triangle.get(i + 1).get(j + 1);   8                 list.set(j, list.get(j) + min); 9             }10         }11         return triangle.get(0).get(0);12     }

This code was previously seen and very powerful.