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.

元素的下一个只能是相邻的最小元素，如3的下一个元素是6，5中的一个。如此

求出从上到下的最小值路径。

构建一个n的数组，初始化为最后一行元素，从下向上更新数组值。

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