Substring Search Patterns in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the pattern exists in the text using includes method.

DSA Typescript

const text = "hello world";
const pattern = "world";
const found = text.[1](pattern);
console.log(found);

Drag options to blanks, or click blank then click option'

Asearch

Bincludes

CindexOf

Dmatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using indexOf returns a number, not a boolean.

Using search returns an index or -1, not a boolean.

The includes() method returns true if the pattern is found in the text, otherwise false.

2fill in blank

medium

Complete the code to find the first index of the pattern in the text.

DSA Typescript

const text = "abracadabra";
const pattern = "cad";
const index = text.[1](pattern);
console.log(index);

Drag options to blanks, or click blank then click option'

AindexOf

Bincludes

Csearch

Dmatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using includes returns boolean, not index.

Using match returns an array, not index.

indexOf returns the first index where the pattern starts or -1 if not found.

3fill in blank

hard

Fix the error in the code to correctly find all occurrences of the pattern using RegExp.

DSA Typescript

const text = "banana";
const pattern = /an/g;
const matches = text.[1](pattern);
console.log(matches);

Drag options to blanks, or click blank then click option'

Amatch

BmatchAll

Csearch

DindexOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using matchAll returns an iterator, not an array.

Using search returns only first match index.

The match() method with global flag returns all matches as an array.

4fill in blank

hard

Fill both blanks to create a function that returns all start indices of the pattern in the text.

DSA Typescript

function findAllIndices(text: string, pattern: string): number[] {
  const indices: number[] = [];
  let pos = text.[1](pattern);
  while (pos !== [2]) {
    indices.push(pos);
    pos = text.indexOf(pattern, pos + 1);
  }
  return indices;
}

Drag options to blanks, or click blank then click option'

AindexOf

Bincludes

C-1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using includes returns boolean, not index.

Comparing pos to 0 instead of -1 causes infinite loop.

indexOf finds the first occurrence; -1 means no more occurrences.

5fill in blank

hard

Fill all three blanks to create a function that returns a map of each pattern to its count in the text.

DSA Typescript

function countPatterns(text: string, patterns: string[]): Record<string, number> {
  const counts: Record<string, number> = {};
  for (const pattern of patterns) {
    counts[[1]] = 0;
    let pos = text.indexOf(pattern);
    while (pos !== [2]) {
      counts[pattern] += [3];
      pos = text.indexOf(pattern, pos + 1);
    }
  }
  return counts;
}

Drag options to blanks, or click blank then click option'

Apattern

B-1

C1

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Using text as key instead of pattern.

Incrementing count by wrong value.

Checking pos against 0 instead of -1.

Use pattern as key, -1 to check no more matches, and increment count by 1.

Practice

1. What is the main goal of substring search algorithms in strings?

easy

A. To sort all characters in a string alphabetically

B. To find if a smaller string exists inside a larger string

C. To reverse the entire string

D. To count the total number of vowels in a string

Solution

1. Step 1: Understand substring search purpose

   Substring search algorithms check if a smaller string (pattern) appears inside a bigger string (text).

2. Step 2: Compare options with substring search definition

   Only To find if a smaller string exists inside a larger string matches this goal. Sorting, reversing, or counting vowels are different tasks.

3. Final Answer:

   To find if a smaller string exists inside a larger string -> Option B

4. Quick Check:

   Substring search = find smaller string inside larger [OK]

Hint: Substring search means finding a smaller string inside a bigger one [OK]

Common Mistakes:

• Confusing substring search with sorting or reversing strings
• Thinking substring search counts characters
• Mixing substring search with string length calculation

2. Which of the following is the correct TypeScript syntax to check if string text contains substring pattern?

easy

A. text.includes(pattern)

B. text.contains(pattern)

C. text.has(pattern)

D. text.find(pattern)

Solution

1. Step 1: Recall TypeScript string methods

   TypeScript strings have a method called includes to check substring presence.

2. Step 2: Verify method names

   Only includes is valid. contains, has, and find are not string methods in TypeScript.

3. Final Answer:

   text.includes(pattern) -> Option A

4. Quick Check:

   Use includes() to check substring presence [OK]

Hint: Use includes() method to check substring in TypeScript [OK]

Common Mistakes:

• Using non-existent methods like contains() or has()
• Confusing includes() with find() which is for arrays
• Forgetting parentheses after method name

3. What will be the output of the following TypeScript code?

const text = "hello world";
const pattern = "wor";
console.log(text.indexOf(pattern));

medium

A. 6

B. -1

C. 3

D. 0

Solution

1. Step 1: Understand indexOf method

   indexOf returns the starting index of the substring if found, else -1.

2. Step 2: Find substring position in text

   In "hello world", substring "wor" starts at index 6 (0-based counting: h=0, e=1, l=2, l=3, o=4, space=5, w=6).

3. Final Answer:

   6 -> Option A

4. Quick Check:

   indexOf("wor") = 6 [OK]

Hint: indexOf returns start index or -1 if not found [OK]

Common Mistakes:

• Counting index starting from 1 instead of 0
• Confusing indexOf with includes (which returns boolean)
• Assuming indexOf returns substring length

4. Identify the error in the following TypeScript code snippet for substring search:

const text = "typescript";
const pattern = "script";
if (text.find(pattern)) {
  console.log("Found");
} else {
  console.log("Not Found");
}

medium

A. Using if statement without parentheses

B. Missing semicolon after console.log statements

C. Pattern variable is not declared

D. Using find() method on string which does not exist

Solution

1. Step 1: Check string methods in TypeScript

   Strings do not have a find() method. The correct method to check substring is includes() or indexOf().

2. Step 2: Verify other code parts

   Semicolons are optional in TypeScript, pattern is declared, and if statement syntax is correct.

3. Final Answer:

   Using find() method on string which does not exist -> Option D

4. Quick Check:

   Strings have includes(), not find() [OK]

Hint: Use includes() or indexOf(), not find() on strings [OK]

Common Mistakes:

• Assuming find() works on strings like arrays
• Thinking semicolons are mandatory causing errors
• Misreading if statement syntax

5. You want to find all starting indices of substring pattern in string text. Which approach correctly finds multiple occurrences in TypeScript?

hard

A. Use text.indexOf(pattern) once and return that single index

B. Use text.includes(pattern) repeatedly without changing index

C. Use a loop with indexOf(pattern, startIndex) updating startIndex after each find

D. Use text.findAll(pattern) method to get all indices

Solution

1. Step 1: Understand multiple substring search

   To find all occurrences, you must repeatedly search starting after the last found index.

2. Step 2: Analyze each option

   Use a loop with indexOf(pattern, startIndex) updating startIndex after each find uses a loop with indexOf and updates start index, which is correct. Use text.includes(pattern) repeatedly without changing index does not update index, so it loops infinitely or finds only once. Use text.indexOf(pattern) once and return that single index finds only one occurrence. Use text.findAll(pattern) method to get all indices uses a non-existent method.

3. Final Answer:

   Use a loop with indexOf(pattern, startIndex) updating startIndex after each find -> Option C

4. Quick Check:

   Loop with indexOf and updated start index finds all [OK]

Hint: Loop with indexOf and update start index to find all [OK]

Common Mistakes:

• Not updating start index causing infinite loops
• Using includes() which returns boolean, not index
• Expecting findAll() method which does not exist