String Manipulation in C#: Finding Substring Occurrences

Introduction

Hello, and welcome to our analysis lesson. Today, we will explore a classic problem in the realm of string manipulations . We'll learn how to locate all occurrences of a substring within a larger string using C# . The techniques you will learn can be used in scenarios such as text processing and data analysis. Are you ready to dive in? Let's get started!

Task Statement and Description

Here's our challenge: we have two lists of strings of the same length, one containing the "original" strings and the other, the "substrings." We're to identify all occurrences of each substring within its corresponding original string and return a list of the starting indices of these occurrences. Remember, index counting should start from 0. Example If we take the following lists: Original List: new List<string> { "HelloWorld", "LearningCSharp", "GoForBroke", "BackToBasics" } Substring List: new List<string> { "loW", "ear", "o", "Ba" } . This will produce the following outputs: In "HelloWorld", "loW" starts at index 3. In "LearningCSharp", "ear" starts at index 1. In "GoForBroke", "o" appears at indices 1, 3, and 7. In "BackToBasics", "Ba" starts at indices 0 and 6. So, if FindSubString(new List<string> { "HelloWorld", "LearningCSharp", "GoForBroke", "BackToBasics" }, new List<string> { "loW", "ear", "o", "Ba" }) is called, 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 'LearningCSharp' 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."] ["The substring 'loW' was found in the original string 'HelloWorld' at position(s) 3.", "The substring 'ear' was found in the original string 'LearningCSharp' 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 seems reasonably straightforward, it may still feel daunting. Fear not! We will dissect it piece by piece.

Step-by-Step Solution: Initializing the Output

First, we need to create a place to store the result of our findings. Can you think of a C# data type that we could use for that? That's correct — a List<string> would be perfect for this task! C# public static List<string> Solution(List<string> origStrs, List<string> substrs) {List<string> resultArr = new List<string>();}

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[
    "The substring 'loW' was found in the original string 'HelloWorld' at position(s) 3.",
    "The substring 'ear' was found in the original string 'LearningCSharp' 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."
]

for (int i = 0; i < origStrs.Count; i++)
{
    string original = origStrs[i];
    string substring = substrs[i];
    int startPos = original.IndexOf(substring);
}

for (int i = 0; i < origStrs.Count; i++)
{
    string original = origStrs[i];
    string substring = substrs[i];
    int startPos = original.IndexOf(substring);
}

    List<string> matchIndices = new List<string>();
    while (startPos != -1)
    {
        matchIndices.Add(startPos.ToString());
        startPos = original.IndexOf(substring, startPos + 1);
    }

    List<string> matchIndices = new List<string>();
    while (startPos != -1)
    {
        matchIndices.Add(startPos.ToString());
        startPos = original.IndexOf(substring, startPos + 1);
    }

{
    resultArr.Add($"The substring '{substring}' was found in the original string '{original}' at position(s) {string.Join(", ", matchIndices)}.");
}

{
    resultArr.Add($"The substring '{substring}' was found in the original string '{original}' at position(s) {string.Join(", ", matchIndices)}.");
}

using System;
using System.Collections.Generic;

public class Program
{
    public static List<string> Solution(List<string> origStrs, List<string> substrs)
    {
        List<string> resultArr = new List<string>();

        for (int i = 0; i < origStrs.Count; i++)
        {
            string original = origStrs[i];
            string substring = substrs[i];
            int startPos = original.IndexOf(substring);
            List<string> matchIndices = new List<string>();

            while (startPos != -1)
            {
                matchIndices.Add(startPos.ToString());
                startPos = original.IndexOf(substring, startPos + 1);
            }

            resultArr.Add($"The substring '{substring}' was found in the original string '{original}' at position(s) {string.Join(", ", matchIndices)}.");
        }

        return resultArr;
    }

    public static void Main()
    {
        List<string> originalList = new List<string> { "HelloWorld", "LearningCSharp", "GoForBroke", "BackToBasics" };
        List<string> substringList = new List<string> { "loW", "ear", "o", "Ba" };
        List<string> results = Solution(originalList, substringList);

        foreach (var result in results)
        {
            Console.WriteLine(result);
        // Expected Output:
        // The substring 'loW' was found in the original string 'HelloWorld' at position(s) 3.
        // The substring 'ear' was found in the original string 'LearningCSharp' 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.
        }
    }
}

using System;
using System.Collections.Generic;

public class Program
{
    public static List<string> Solution(List<string> origStrs, List<string> substrs)
    {
        List<string> resultArr = new List<string>();

        for (int i = 0; i < origStrs.Count; i++)
        {
            string original = origStrs[i];
            string substring = substrs[i];
            int startPos = original.IndexOf(substring);
            List<string> matchIndices = new List<string>();

            while (startPos != -1)
            {
                matchIndices.Add(startPos.ToString());
                startPos = original.IndexOf(substring, startPos + 1);
            }

            resultArr.Add($"The substring '{substring}' was found in the original string '{original}' at position(s) {string.Join(", ", matchIndices)}.");
        }

        return resultArr;
    }

    public static void Main()
    {
        List<string> originalList = new List<string> { "HelloWorld", "LearningCSharp", "GoForBroke", "BackToBasics" };
        List<string> substringList = new List<string> { "loW", "ear", "o", "Ba" };
        List<string> results = Solution(originalList, substringList);

        foreach (var result in results)
        {
            Console.WriteLine(result);
        // Expected Output:
        // The substring 'loW' was found in the original string 'HelloWorld' at position(s) 3.
        // The substring 'ear' was found in the original string 'LearningCSharp' 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.
        }
    }
}

for (int i = 0; i < origStrs.Count; i++)
{
    string original = origStrs[i];
    string substring = substrs[i];
    int startPos = original.IndexOf(substring);
}

    List<string> matchIndices = new List<string>();
    while (startPos != -1)
    {
        matchIndices.Add(startPos.ToString());
        startPos = original.IndexOf(substring, startPos + 1);
    }

{
    resultArr.Add($"The substring '{substring}' was found in the original string '{original}' at position(s) {string.Join(", ", matchIndices)}.");
}

using System;
using System.Collections.Generic;

public class Program
{
    public static List<string> Solution(List<string> origStrs, List<string> substrs)
    {
        List<string> resultArr = new List<string>();

        for (int i = 0; i < origStrs.Count; i++)
        {
            string original = origStrs[i];
            string substring = substrs[i];
            int startPos = original.IndexOf(substring);
            List<string> matchIndices = new List<string>();

            while (startPos != -1)
            {
                matchIndices.Add(startPos.ToString());
                startPos = original.IndexOf(substring, startPos + 1);
            }

            resultArr.Add($"The substring '{substring}' was found in the original string '{original}' at position(s) {string.Join(", ", matchIndices)}.");
        }

        return resultArr;
    }

    public static void Main()
    {
        List<string> originalList = new List<string> { "HelloWorld", "LearningCSharp", "GoForBroke", "BackToBasics" };
        List<string> substringList = new List<string> { "loW", "ear", "o", "Ba" };
        List<string> results = Solution(originalList, substringList);

        foreach (var result in results)
        {
            Console.WriteLine(result);
        // Expected Output:
        // The substring 'loW' was found in the original string 'HelloWorld' at position(s) 3.
        // The substring 'ear' was found in the original string 'LearningCSharp' 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.
        }
    }
}

Introduction

Task Statement and Description

Step-by-Step Solution: Initializing the Output

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Pairing Strings and Finding First Occurrence

Finding Subsequent Occurrences

Formatting and Storing the Results

The Final Solution

Lesson Summary