[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.

import java.util.ArrayList;public class Solution {    public int minimumTotal(List<List<Integer>> triangle) {        if(triangle == null || triangle.size() == 0) return 0;        int n = triangle.size();        int[][] sum = new int[n][n];        for(int i = 0; i < n; i++){            sum[n - 1][i] = triangle.get(n - 1).get(i);        }        for(int i = n - 2; i >= 0; i--){            for(int j = 0; j <= i; j++){                sum[i][j] = Math.min(sum[i + 1][j], sum[i + 1][j + 1]) + triangle.get(i).get(j);            }        }        return sum[0][0];    }}