Home Backend Development PHP Tutorial Extra Characters in a String

Extra Characters in a String

Sep 23, 2024 pm 04:16 PM

Extra Characters in a String

2707. Extra Characters in a String

Difficulty: Medium

Topics: Array, Hash Table, String, Dynamic Programming, Trie

You are given a 0-indexed string s and a dictionary of words dictionary. You have to break s into one or more non-overlapping substrings such that each substring is present in dictionary. There may be some extra characters in s which are not present in any of the substrings.

Return the minimum number of extra characters left over if you break up s optimally.

Example 1:

  • Input: s = "leetscode", dictionary = ["leet","code","leetcode"]
  • Output: 1
  • Explanation: We can break s in two substrings: "leet" from index 0 to 3 and "code" from index 5 to 8. There is only 1 unused character (at index 4), so we return 1.

Example 2:

  • Input: s = "sayhelloworld", dictionary = ["hello","world"]
  • Output: 3
  • Explanation: We can break s in two substrings: "hello" from index 3 to 7 and "world" from index 8 to 12. The characters at indices 0, 1, 2 are not used in any substring and thus are considered as extra characters. Hence, we return 3.

Constraints:

  • 1 <= s.length <= 50
  • 1 <= dictionary.length <= 50
  • 1 <= dictionary[i].length <= 50
  • dictionary[i] and s consists of only lowercase English letters
  • dictionary contains distinct words

Hint:

  1. Can we use Dynamic Programming here?
  2. Define DP[i] as the min extra character if breaking up s[0:i] optimally.

Solution:

We can define a dp array where dp[i] represents the minimum number of extra characters in the substring s[0:i] after optimal segmentation.

Approach:

  1. Dynamic Programming Definition:

    • Let dp[i] be the minimum number of extra characters in the substring s[0:i].
    • To calculate dp[i], we can:
      • Either consider the character s[i-1] as an extra character and move to the next index.
      • Or check if some substring ending at index i exists in the dictionary, and if it does, then use it to reduce extra characters.
  2. Transition:

    • For each index i, we either:
      • Add one to dp[i-1] if we treat s[i] as an extra character.
      • Check every possible substring s[j:i] (for j < i) and if s[j:i] is in the dictionary, we update dp[i] based on dp[j].
  3. Result:

    • The value of dp[len(s)] will give us the minimum number of extra characters in the entire string s.

Let's implement this solution in PHP: 2707. Extra Characters in a String






Explanation:

  1. Base Case:

    • dp[0] = 0 since no extra characters exist in an empty string.
  2. Dictionary Lookup:

    • We store the dictionary words in a hash map using array_flip() for constant-time lookup.
  3. Transition:

    • For each position i, we check all possible substrings s[j:i]. If a substring exists in the dictionary, we update the dp[i] value.
  4. Time Complexity:

    • The time complexity is O(n^2) where n is the length of the string s because for each index, we check all previous indices to form substrings.

Test Results:

For the input "leetscode" with dictionary ["leet","code","leetcode"], the function correctly returns 1, as only 1 extra character ("s") remains.

For the input "sayhelloworld" with dictionary ["hello","world"], the function returns 3, as the first three characters ("say") are extra.

Contact Links

If you found this series helpful, please consider giving the repository a star on GitHub or sharing the post on your favorite social networks ?. Your support would mean a lot to me!

If you want more helpful content like this, feel free to follow me:

  • LinkedIn
  • GitHub

The above is the detailed content of Extra Characters in a String. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Hot Topics

Java Tutorial
1664
14
PHP Tutorial
1268
29
C# Tutorial
1246
24
PHP and Python: Comparing Two Popular Programming Languages PHP and Python: Comparing Two Popular Programming Languages Apr 14, 2025 am 12:13 AM

PHP and Python each have their own advantages, and choose according to project requirements. 1.PHP is suitable for web development, especially for rapid development and maintenance of websites. 2. Python is suitable for data science, machine learning and artificial intelligence, with concise syntax and suitable for beginners.

PHP in Action: Real-World Examples and Applications PHP in Action: Real-World Examples and Applications Apr 14, 2025 am 12:19 AM

PHP is widely used in e-commerce, content management systems and API development. 1) E-commerce: used for shopping cart function and payment processing. 2) Content management system: used for dynamic content generation and user management. 3) API development: used for RESTful API development and API security. Through performance optimization and best practices, the efficiency and maintainability of PHP applications are improved.

Explain secure password hashing in PHP (e.g., password_hash, password_verify). Why not use MD5 or SHA1? Explain secure password hashing in PHP (e.g., password_hash, password_verify). Why not use MD5 or SHA1? Apr 17, 2025 am 12:06 AM

In PHP, password_hash and password_verify functions should be used to implement secure password hashing, and MD5 or SHA1 should not be used. 1) password_hash generates a hash containing salt values ​​to enhance security. 2) Password_verify verify password and ensure security by comparing hash values. 3) MD5 and SHA1 are vulnerable and lack salt values, and are not suitable for modern password security.

PHP: A Key Language for Web Development PHP: A Key Language for Web Development Apr 13, 2025 am 12:08 AM

PHP is a scripting language widely used on the server side, especially suitable for web development. 1.PHP can embed HTML, process HTTP requests and responses, and supports a variety of databases. 2.PHP is used to generate dynamic web content, process form data, access databases, etc., with strong community support and open source resources. 3. PHP is an interpreted language, and the execution process includes lexical analysis, grammatical analysis, compilation and execution. 4.PHP can be combined with MySQL for advanced applications such as user registration systems. 5. When debugging PHP, you can use functions such as error_reporting() and var_dump(). 6. Optimize PHP code to use caching mechanisms, optimize database queries and use built-in functions. 7

How does PHP handle file uploads securely? How does PHP handle file uploads securely? Apr 10, 2025 am 09:37 AM

PHP handles file uploads through the $\_FILES variable. The methods to ensure security include: 1. Check upload errors, 2. Verify file type and size, 3. Prevent file overwriting, 4. Move files to a permanent storage location.

How does PHP type hinting work, including scalar types, return types, union types, and nullable types? How does PHP type hinting work, including scalar types, return types, union types, and nullable types? Apr 17, 2025 am 12:25 AM

PHP type prompts to improve code quality and readability. 1) Scalar type tips: Since PHP7.0, basic data types are allowed to be specified in function parameters, such as int, float, etc. 2) Return type prompt: Ensure the consistency of the function return value type. 3) Union type prompt: Since PHP8.0, multiple types are allowed to be specified in function parameters or return values. 4) Nullable type prompt: Allows to include null values ​​and handle functions that may return null values.

The Enduring Relevance of PHP: Is It Still Alive? The Enduring Relevance of PHP: Is It Still Alive? Apr 14, 2025 am 12:12 AM

PHP is still dynamic and still occupies an important position in the field of modern programming. 1) PHP's simplicity and powerful community support make it widely used in web development; 2) Its flexibility and stability make it outstanding in handling web forms, database operations and file processing; 3) PHP is constantly evolving and optimizing, suitable for beginners and experienced developers.

PHP vs. Python: Understanding the Differences PHP vs. Python: Understanding the Differences Apr 11, 2025 am 12:15 AM

PHP and Python each have their own advantages, and the choice should be based on project requirements. 1.PHP is suitable for web development, with simple syntax and high execution efficiency. 2. Python is suitable for data science and machine learning, with concise syntax and rich libraries.

See all articles