Substring Search Patterns in DSA Python - Build from Scratch

Substring Search Patterns

📖 Scenario: You are building a simple text search tool that helps users find specific words inside a paragraph. This is useful for searching keywords in documents, notes, or messages.

🎯 Goal: Build a program that searches for a given substring inside a text and shows all the starting positions where the substring appears.

📋 What You'll Learn

Create a string variable with a fixed paragraph of text.

Create a string variable for the substring to search.

Use a loop to find all starting indexes where the substring appears in the text.

Print the list of all starting positions.

💡 Why This Matters

🌍 Real World

Searching for keywords in documents, emails, or chat messages to quickly find important information.

💼 Career

Substring search is a basic skill used in text processing, search engines, and data analysis roles.

1

Create the text to search

Create a string variable called text with the exact value: 'the quick brown fox jumps over the lazy dog'

DSA Python

# Create the text variable
# Your code here

Hint

Use single quotes to create the string exactly as shown.

2

Set the substring to search

Create a string variable called pattern with the exact value: 'the'

DSA Python

text = 'the quick brown fox jumps over the lazy dog'
# Create the pattern variable
# Your code here

Hint

Use single quotes to create the string exactly as shown.

3

Find all starting positions of the substring

Create an empty list called positions. Use a for loop with variable i to check every index in text where pattern could start. If the substring of text from i to i + len(pattern) equals pattern, append i to positions.

DSA Python

text = 'the quick brown fox jumps over the lazy dog'
pattern = 'the'
# Find all positions where pattern appears
# Your code here

Hint

Use slicing to get the substring from i to i + len(pattern).

4

Print the list of starting positions

Use print(positions) to display the list of all starting positions where pattern appears in text.

DSA Python

text = 'the quick brown fox jumps over the lazy dog'
pattern = 'the'
positions = []
for i in range(len(text) - len(pattern) + 1):
    if text[i:i+len(pattern)] == pattern:
        positions.append(i)
# Print the positions list
# Your code here

Hint

The output should be a list of integers showing where 'the' starts in the text.