Substring Search in C++: A Comprehensive Guide

Introduction

Hello, and welcome to our analysis lesson. Today, we will be tackling a common problem in the field of string manipulations with C++ . We will learn how to find all occurrences of a substring within a larger string . The techniques you will master today can be utilized in numerous situations, such as text processing and data analysis. Are you ready to get started? Let's jump right in!

Task Statement and Description

Here is the task for today: We have two vectors of strings, both of identical lengths — the first containing the "original" strings and the second containing the substrings . Our goal is to detect all occurrences of each substring within its corresponding original string and, finally, return a vector that contains the starting indices of these occurrences. Remember, the index counting should start from 0. Example Let's consider the following vectors: Original Vector: { "HelloWorld", "LearningC++", "GoForBroke", "BackToBasics" } Substring Vector: { "loW", "ear", "o", "Ba" } . The following are the expected outputs: In "HelloWorld", "loW" starts at index 3. In "LearningC++", "ear" starts at index 1. In "GoForBroke", "o" appears at indices 1, 3, and 7. In "BackToBasics", "Ba" starts at indices 0 and 6. Thus, when findSubString({"HelloWorld", "LearningC++", "GoForBroke", "BackToBasics"}, {"loW", "ear", "o", "Ba"}) is invoked, the function should return {"The substring 'loW' was found in the original string 'HelloWorld' at position(s) 3.", "The substring 'ear' was found in the original string 'LearningC++' at position(s) 1.", "The substring 'o' was found in the original string 'GoForBroke' at position(s) 1, 3, 7.", "The substring 'Ba' was found in the original string 'BackToBasics' at position(s) 0, 6."} Although this task may seem fairly straightforward, it can prove challenging. However, don't worry! We will break it down step by step.

Step-by-Step Solution: Step 1, Creating the Output Vector

Initially, we need to create a space to store our results. Can you think of a C++ data type that would be ideal for this task? That's right! A vector would be perfect! C++std::vector<std::string> solution(std::vector<std::string> orig_strs, std::vector<std::string> substrs) { std::vector<std::string> result;

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C++

    for (size_t i = 0; i < orig_strs.size(); ++i) {
        size_t start_pos = orig_strs[i].find(substrs[i]);

C++

        std::vector<size_t> match_indices;
        while (start_pos != std::string::npos) {
            match_indices.push_back(start_pos);
            start_pos = orig_strs[i].find(substrs[i], start_pos + substrs[i].size());
        }

C++

        std::ostringstream os;
        os << "The substring '" << substrs[i] << "' was found in the original string '" << orig_strs[i] << "' at position(s) ";
        for (size_t idx : match_indices)
            os << idx << ", ";
        os.seekp(-2, os.cur);  // remove trailing comma and space
        os << ".";
        result.push_back(os.str());
    }

C++

#include <vector>
#include <string>
#include <sstream>
#include <iostream>

std::vector<std::string> solution(std::vector<std::string> orig_strs, std::vector<std::string> substrs) {
    std::vector<std::string> result;

    for (size_t i = 0; i < orig_strs.size(); ++i) {
        size_t start_pos = orig_strs[i].find(substrs[i]);
        std::vector<size_t> match_indices;

        while (start_pos != std::string::npos) {
            match_indices.push_back(start_pos);
            start_pos = orig_strs[i].find(substrs[i], start_pos + substrs[i].size());
        }

        std::ostringstream os;
        os << "The substring '" << substrs[i] << "' was found in the original string '" << orig_strs[i] << "' at position(s) ";
        for (size_t idx : match_indices)
            os << idx << ", ";
        os.seekp(-2, os.cur);  // remove trailing comma and space
        os << ".";
        result.push_back(os.str());
    }

    return result;
}

int main() {
    // Call the function
    std::vector<std::string> result = solution({ "HelloWorld", "LearningC++", "GoForBroke", "BackToBasics" }, { "loW", "ear", "o", "Ba" });
    for (int i = 0; i < result.size(); ++i) {
        std::cout << result[i] << std::endl;
    }
    return 0;
}

Introduction

Task Statement and Description

Step-by-Step Solution: Step 1, Creating the Output Vector

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Step 2: Pairing Strings and Locating First Occurrence

Step 3: Locating Subsequent Occurrences

Step 4: Formatting and Storing the Results

The Complete Solution

Lesson Summary