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.

采用自下而上的dp思路

public class Solution {
    public int minimumTotal(List<List<Integer>> triangle) {
        int[] total = new int[triangle.size()];
         int l = triangle.size() - 1;
 
    for (int i = 0; i < triangle.get(l).size(); i++) {
        total[i] = triangle.get(l).get(i);
    }
 
    // iterate from last second row
    for (int i = triangle.size() - 2; i >= 0; i--) {
        for (int j = 0; j < triangle.get(i + 1).size() - 1; j++) {
            total[j] = triangle.get(i).get(j) + Math.min(total[j], total[j + 1]);
        }
    }
 
    return total[0];
    }
}

参考链接：http://www.programcreek.com/2013/01/leetcode-triangle-java/