LeetCode 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.

题意：数塔求最小的路径和是多少。

思路：数塔的DP思想，为了不妨碍后面的计算，我们每行计算从后面开始。

public class Solution {    public int minimumTotal(List<List<Integer>> triangle) {        int n = triangle.size();    if (n == 0) return 0;        int f[] = new int[triangle.size()];    f[0]=  triangle.get(0).get(0);    for (int i = 1; i < triangle.size(); i++)     for (int j = triangle.get(i).size()-1; j >= 0; j--) {    if (j == 0)     f[j] = f[j] + triangle.get(i).get(j);    else if (j == triangle.get(i).size() - 1)     f[j] = f[j-1] + triangle.get(i).get(j);    else f[j] = Math.min(f[j-1], f[j]) + triangle.get(i).get(j);     }        int ans = Integer.MAX_VALUE;    for (int i = 0; i < f.length; i++)    ans = Math.min(ans, f[i]);        return ans;    }}