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.
从底层开始，每往上一层，上面一层的每个节点会选择其子节点中较小的一个，再往上，就是每个节点会选择子路径中较小的一个，代码如下：
public class Solution {    public int minimumTotal(List<List<Integer>> triangle) {        int[] res = new int[triangle.size() + 1];        for (int i = triangle.size() - 1; i >= 0; i --) {            for (int j = 0; j < triangle.get(i).size(); j ++) {                res[j] = triangle.get(i).get(j) + Math.min(res[j], res[j + 1]);            }        }        return res[0];    }}