Triangle

最新推荐文章于 2023-05-05 10:12:11 发布

cgdong2014

最新推荐文章于 2023-05-05 10:12:11 发布

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分类专栏： LeetCode

本文链接：https://blog.youkuaiyun.com/cgdong2014/article/details/39570831

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本文介绍了一种求解从三角形顶部到底部的最小路径和的问题，通过自底向上的动态规划方法实现，最终返回从顶部到底部的最小路径总和。

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： From bottom to the top. Every time select the buffer[j] = Math.min(buffer[j], buffer[j + 1]) + cur.get(j); At last return buffer[0];

易错点：注意次序和 SIZE

public class Solution {
    public int minimumTotal(List<List<Integer>> triangle) {
        int len = triangle.size();
        int[] buffer = new int[len];
        List<Integer> bottom = triangle.get(len - 1);
        for(int i = 0; i < len; i++){
            buffer[i] = bottom.get(i);
        }
        
        for(int i = len - 2; i >= 0; i--){
            List<Integer> cur = triangle.get(i);
            for(int j = 0; j < cur.size(); j++){
                buffer[j] = Math.min(buffer[j], buffer[j+1]) + cur.get(j);
            }
        }
        return buffer[0];
    }
}