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LeetCode

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Problem

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.

Code

从下往上遍历就不用再遍历最后一行了

class Solution {
    public int minimumTotal(List<List<Integer>> triangle) {
        for(int i = triangle.size() - 2; i >= 0; i--) {
            List<Integer> curr = triangle.get(i);
            for(int j = 0; j <= i; j++){
                int nextRow1 = triangle.get(i + 1).get(j);
                int nextRow2 = triangle.get(i + 1).get(j + 1);

                curr.set(j, Math.min(nextRow1, nextRow2) + curr.get(j));
            }
        }

        return triangle.get(0).get(0);
    }
}