Substring Extraction

A Substring is a contiguous sequence of characters contained within a larger parent string. For example, "gram" is a substring of "Programming". Extracting a substring is a key operation in text processing, parsing, and lexical analysis.

Implementation Mechanics

In Static/Low-level Languages (like C): Substring extraction requires allocating a target buffer (with enough capacity plus 1 extra byte for the null-terminator), then copying characters one-by-one from the source array starting at index start up to start + length, and manually assigning the null-terminator '\0' at the end.
In Object-Oriented Languages (like C++): The standard library provides the .substr(start, length) method, which handles memory management and returns a new std::string object.
In Managed/Immutable Systems (like Java/JavaScript): Methods like .substring(beginIndex, endIndex) are available. In older Java runtimes, substrings shared the parent string's character array to save memory, which could lead to memory leaks if a tiny substring kept a huge parent string in memory. Modern runtimes create a clean new copy to avoid this.

Complexity Analysis

Time Complexity:
- Best/Worst/Average Case: O(K) (where K is the length of the extracted substring, since we must copy exactly K characters)
Space Complexity: O(K) (to store the extracted substring in memory)