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.
思路:数塔的DP思想,为了最好还是碍后面的计算。我们每行计算从后面開始。
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; } }