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Posts tagged as “hashtable”

花花酱 LeetCode 760. Find Anagram Mappings

题目大意:输出数组A中每个元素在数组B中的索引。

Given two lists Aand B, and B is an anagram of AB is an anagram of A means B is made by randomizing the order of the elements in A.

We want to find an index mapping P, from A to B. A mapping P[i] = j means the ith element in A appears in B at index j.

These lists A and B may contain duplicates. If there are multiple answers, output any of them.

For example, given

We should return

as P[0] = 1 because the 0th element of A appears at B[1], and P[1] = 4 because the 1st element of Aappears at B[4], and so on.

Solution:

C++

Time complexity: O(nlogn)

Space complexity: O(n)

C++ / No duplication

 

花花酱 LeetCode 734. Sentence Similarity

Problem:

Given two sentences words1, words2 (each represented as an array of strings), and a list of similar word pairs pairs, determine if two sentences are similar.

For example, “great acting skills” and “fine drama talent” are similar, if the similar word pairs are pairs = [["great", "fine"], ["acting","drama"], ["skills","talent"]].

Note that the similarity relation is not transitive. For example, if “great” and “fine” are similar, and “fine” and “good” are similar, “great” and “good” are not necessarily similar.

However, similarity is symmetric. For example, “great” and “fine” being similar is the same as “fine” and “great” being similar.

Also, a word is always similar with itself. For example, the sentences words1 = ["great"], words2 = ["great"], pairs = [] are similar, even though there are no specified similar word pairs.

Finally, sentences can only be similar if they have the same number of words. So a sentence like words1 = ["great"] can never be similar to words2 = ["doubleplus","good"].

Note:

  • The length of words1 and words2 will not exceed 1000.
  • The length of pairs will not exceed 2000.
  • The length of each pairs[i] will be 2.
  • The length of each words[i] and pairs[i][j] will be in the range [1, 20].


题目大意:

给你两个句子(由单词数组表示)和一些近义词对,问你这两个句子是否相似,即每组相对应的单词都要相似。

注意相似性不能传递,比如给只你”great”和”fine”相似、”fine”和”good”相似,这种情况下”great”和”good”不相似。

Idea:

Use hashtable to store mapping from word to its similar words.

Solution: HashTable

Time complexity: O(|pairs| + |words1|)

Space complexity: O(|pairs|)

C++

Java

Python

Related Problems:

花花酱 LeetCode 1. Two Sum

Problem:

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

Idea:

Brute force / Hashtable

Solution1:

Brute force / C++

Time complexity: O(n^2)

Space complexity: O(1)

Solution 2:

Hashtable / C++

Time complexity: O(n)

Space complexity: O(n)

 

 

花花酱 LeetCode 128. Longest Consecutive Sequence

 

Problem:

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

For example,
Given [100, 4, 200, 1, 3, 2],
The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length: 4.

Your algorithm should run in O(n) complexity.



Idea:

Hashtable / Hashset

 

Time complexity: O(n)

Space complexity: O(n)

Solution 1: C++ / online

 

Solution 2: C++ / offline

 

花花酱 LeetCode 208. Implement Trie (Prefix Tree)

Problem:

Implement a trie with insertsearch, and startsWith methods.

Note:
You may assume that all inputs are consist of lowercase letters a-z.

Idea:




Tree/children array

 

 

Solution:

C++ / Array

 

C++ / hashmap

 

Java

 

Python 1:

 

Python 2: