Press "Enter" to skip to content

Huahua's Tech Road

花花酱 LeetCode 687. Longest Univalue Path

题目大意:给你一棵二叉树,返回一条最长的路径,要求路径上所有的节点值都相同。

https://leetcode.com/problems/longest-univalue-path/description/

Problem: 

Given a binary tree, find the length of the longest path where each node in the path has the same value. This path may or may not pass through the root.

Note: The length of path between two nodes is represented by the number of edges between them.

Example 1:

Input:

              5
             / \
            4   5
           / \   \
          1   1   5

Output:

2

Example 2:

Input:

              1
             / \
            4   5
           / \   \
          4   4   5

Output:

2

Note: The given binary tree has not more than 10000 nodes. The height of the tree is not more than 1000.



Idea:

DFS

Solution: Recursion

Time complexity: O(n)

Space complexity: O(n)

C++

Java

Python3

Related Problems

花花酱 LeetCode 678. Valid Parenthesis String

Problem:

Given a string containing only three types of characters: ‘(‘, ‘)’ and ‘*’, write a function to check whether this string is valid. We define the validity of a string by these rules:

  1. Any left parenthesis '(' must have a corresponding right parenthesis ')'.
  2. Any right parenthesis ')' must have a corresponding left parenthesis '('.
  3. Left parenthesis '(' must go before the corresponding right parenthesis ')'.
  4. '*' could be treated as a single right parenthesis ')' or a single left parenthesis '(' or an empty string.
  5. An empty string is also valid.

Example 1:

Example 2:

Example 3:

Note:

  1. The string size will be in the range [1, 100].



Idea:

Dynamic Programming / Counting

Solution 1:

C++ / DP / Top-down O(n^3)

 

C++ / DP/ Bottom-up O(n^3)

 

C++ / Counting O(n)

 

Java / DP / Bottom-up O(n^3)

 

花花酱 LeetCode 683. K Empty Slots

题目大意:有n个花盆,第i天,第flowers[i]个花盆的花会开。问是否存在一天,两朵花之间有k个空花盆。

Problem:

There is a garden with N slots. In each slot, there is a flower. The N flowers will bloom one by one in N days. In each day, there will be exactly one flower blooming and it will be in the status of blooming since then.

Given an array flowers consists of number from 1 to N. Each number in the array represents the place where the flower will open in that day.

For example, flowers[i] = x means that the unique flower that blooms at day i will be at position x, where i and x will be in the range from 1 to N.

Also given an integer k, you need to output in which day there exists two flowers in the status of blooming, and also the number of flowers between them is k and these flowers are not blooming.

If there isn’t such day, output -1.

Example 1:

Input: 
flowers: [1,3,2]
k: 1
Output: 2
Explanation: In the second day, the first and the third flower have become blooming.

Example 2:

Input: 
flowers: [1,2,3]
k: 1
Output: -1

Note:

  1. The given array will be in the range [1, 20000].

Idea:

BST/Buckets



 

Solution 2: BST

C++

Solution 3: Buckets

C++

Solution 1: TLE with latest test cases

C++

Java

Python

花花酱 LeetCode 690. Employee Importance

https://leetcode.com/problems/employee-importance/description/

Problem:

ou are given a data structure of employee information, which includes the employee’s unique id, his importance value and his direct subordinates’ id.

For example, employee 1 is the leader of employee 2, and employee 2 is the leader of employee 3. They have importance value 15, 10 and 5, respectively. Then employee 1 has a data structure like [1, 15, [2]], and employee 2 has [2, 10, [3]], and employee 3 has [3, 5, []]. Note that although employee 3 is also a subordinate of employee 1, the relationship is not direct.

Now given the employee information of a company, and an employee id, you need to return the total importance value of this employee and all his subordinates.

Example 1:

Note:

  1. One employee has at most one direct leader and may have several subordinates.
  2. The maximum number of employees won’t exceed 2000.

Idea:

BFS / DFS

Time complexity: O(n)

Space complexity: O(n)

Solution:

C++ / BFS

 

C++ / DFS

 

花花酱 LeetCode 684. Redundant Connection

https://leetcode.com/problems/redundant-connection/description/

Problem:

In this problem, a tree is an undirected graph that is connected and has no cycles.

The given input is a graph that started as a tree with N nodes (with distinct values 1, 2, …, N), with one additional edge added. The added edge has two different vertices chosen from 1 to N, and was not an edge that already existed.

The resulting graph is given as a 2D-array of edges. Each element of edges is a pair [u, v] with u < v, that represents an undirected edge connecting nodes u and v.

Return an edge that can be removed so that the resulting graph is a tree of N nodes. If there are multiple answers, return the answer that occurs last in the given 2D-array. The answer edge [u, v] should be in the same format, with u < v.

Example 1:

Example 2:

Note:

 

  • The size of the input 2D-array will be between 3 and 1000.
  • Every integer represented in the 2D-array will be between 1 and N, where N is the size of the input array.



Idea:
DFS / Union-Find

 

Solutions:

C++ / DFS

 

C++ / Union Find

Java / Union Find

 

Python: Union Find

Python / Union Find V2