Press "Enter" to skip to content

Posts published in “String”

花花酱 LeetCode 745. Prefix and Suffix Search

Link: https://leetcode.com/problems/prefix-and-suffix-search/description/

Problem:

Given many wordswords[i] has weight i.

Design a class WordFilter that supports one function, WordFilter.f(String prefix, String suffix). It will return the word with given prefix and suffix with maximum weight. If no word exists, return -1.

Examples:

Note:

  1. words has length in range [1, 15000].
  2. For each test case, up to words.length queries WordFilter.f may be made.
  3. words[i] has length in range [1, 10].
  4. prefix, suffix have lengths in range [0, 10].
  5. words[i] and prefix, suffix queries consist of lowercase letters only.

Idea:

Construct all possible filters

 

Solution1:

C++

Time complexity: O(NL^3 + QL)  where N is the number of words, L is the max length of the word, Q is the number of queries.

Space complexity: O(NL^3)

Version #2

Solution 2:

C++ / Trie

Time complexity: O(NL^2 + QL)  where N is the number of words, L is the max length of the word, Q is the number of queries.

Space complexity: O(NL^2)

Related Problems:

花花酱 LeetCode 720. Longest Word in Dictionary

Given a list of strings words representing an English Dictionary, find the longest word in words that can be built one character at a time by other words in words. If there is more than one possible answer, return the longest word with the smallest lexicographical order.

If there is no answer, return the empty string.

Example 1:

Example 2:

Note:

 

  • All the strings in the input will only contain lowercase letters.
  • The length of words will be in the range [1, 1000].
  • The length of words[i] will be in the range [1, 30].

Idea:

Brute force

Trie

Solution:

C++

 

 

Trie + Sorting

 

Trie + No sorting

 

花花酱 LeetCode 726. Number of Atoms

 

Problem:

Given a chemical formula (given as a string), return the count of each atom.

An atomic element always starts with an uppercase character, then zero or more lowercase letters, representing the name.

1 or more digits representing the count of that element may follow if the count is greater than 1. If the count is 1, no digits will follow. For example, H2O and H2O2 are possible, but H1O2 is impossible.

Two formulas concatenated together produce another formula. For example, H2O2He3Mg4 is also a formula.

A formula placed in parentheses, and a count (optionally added) is also a formula. For example, (H2O2) and (H2O2)3 are formulas.

Given a formula, output the count of all elements as a string in the following form: the first name (in sorted order), followed by its count (if that count is more than 1), followed by the second name (in sorted order), followed by its count (if that count is more than 1), and so on.

Example 1:

Example 2:

Example 3:

Note:

  • All atom names consist of lowercase letters, except for the first character which is uppercase.
  • The length of formula will be in the range [1, 1000].
  • formula will only consist of letters, digits, and round parentheses, and is a valid formula as defined in the problem.

 



Idea:

Recursion

Time complexity: O(n)

Space complexity: O(n)

Solution:

C++

 

Java

 

花花酱 LeetCode 680. Valid Palindrome II

Problem:

Given a non-empty string s, you may delete at most one character. Judge whether you can make it a palindrome.

Example 1:

Example 2:

Note:

  1. The string will only contain lowercase characters a-z. The maximum length of the string is 50000.

Idea:

Greedy, delete the first unmatched char



Time complexity

O(n)

Solution: