LeetCode Practice Questions

July 21, 2025·

This article provides basic and foundational logic thinking to improve problem solving mindset through solving most frequest asked LeetCode interview questions.

LeetCode Practice Questions

🧮 Math & Number Theory Problems

Sum of N Even Natural Numbers
Check for Even Number
Check for Prime Number
Valid Perfect Square
Decimal to Binary
Binary to Decimal
GCD of Two Numbers

🔢 List & Sequence Problems

Sum of List Elements
Largest Element in a List
Remove Duplicate in a List
Check if All Elements in a List are Unique
Program to Reverse a List
Count Number of Odd and Even Elements in a List
Maximum Difference Between Two Consecutive Elements in a List
Merge Two Sorted Lists
Rotate a List
Merge 2 Lists into Dictionary
Merge Multiple Dictionaries
Words Frequency in a Sentence
Palindromic Tuple
Merge Dictionaries with Common Keys
Check if List is Subset of Another List

📄 String Problems

Reverse a String
Count Vowels in a String
Check for Same Strings
Check Palindrome
Count Words in a String
Remove Duplicates in a String
Count Consonants in a String
Check for Anagrams
Check Subsequence
Check for Substring
Length of the Longest Word

🔷 Pattern Printing Problems

Square of Side ‘N’
Hollow Square of Side ‘N’
Rectangle Pattern
Right Angled Triangle
Inverted Right Angled Triangle
Pyramid Pattern
Inverted Pyramid Pattern
Right Angled Triangle with Numbers
Floyd’s Triangle
Diamond Pattern
Right Angled Triangle II
Sandglass Pattern
Hollow Right Triangle
Hollow Inverted Right Triangle
Number Pyramid Pattern

🧰 Miscellaneous Basic Programs

Celsius to Fahrenheit
Area of a Rectangle
Distance Covered by a Vehicle
Number of Rounds of Lift
Line Equation

Pattern Practice Questions

1. Square of side ‘N’

Input:
N = 4

Output:

****
****
****
****

Constraints: 1 <= N <= 100

2. Hollow Square of side ‘N’

Input:
N = 5

Output:

*****
*   *
*   *
*   *
*****

Constraints: 2 <= N <= 100

3. Rectangle Pattern

Input:
R = 3, C = 6

Output:

******
******
******

Constraints: 1 <= R, C <= 100

4. Right Angled Triangle

Input:
N = 5

Output:

*
**
***
****
*****

Constraints: 1 <= N <= 100

5. Inverted Right Angled Triangle

Input:
N = 5

Output:

*****
****
***
**
*

Constraints: 1 <= N <= 100

6. Pyramid Pattern

Input:
N = 4

Output:

   *
  ***
 *****
*******

Constraints: 1 <= N <= 100

7. Inverted Pyramid Pattern

Input:
N = 4

Output:

*******
 *****
  ***
   *

Constraints: 1 <= N <= 100

8. Right Angled Triangle with Numbers

Input:
N = 5

Output:

Constraints: 1 <= N <= 100

9. Floyd’s Triangle

Input:
N = 5

Output:

1
2 3
4 5 6
7 8 9 10
11 12 13 14 15

Constraints: 1 <= N <= 100

10. Diamond Pattern

Input:
N = 3

Output:

  *
 ***
*****
 ***
  *

Constraints: 1 <= N <= 50

11. Right Angled Triangle II (Alphabets)

Input:
N = 5

Output:

A
A B
A B C
A B C D
A B C D E

Constraints: 1 <= N <= 26

12. Sandglass Pattern

Input:
N = 4

Output:

********
 ******
  ****
   **
   **
  ****
 ******
********

Constraints: 1 <= N <= 50

13. Hollow Right Triangle

Input:
N = 5

Output:

*
**
* *
*  *
*****

Constraints: 2 <= N <= 100

14. Hollow Inverted Right Triangle

Input:
N = 5

Output:

*****
*  *
* *
**
*

Constraints: 2 <= N <= 100

15. Number Pyramid Pattern

Input:
N = 4

Output:

Constraints: 1 <= N <= 100

Functions practice questions

1. 🔥 Celsius to Fahrenheit Converter

Description:
Convert temperature from Celsius to Fahrenheit using the formula:

F = (C × 9/5) + 32

Input:
int C — Temperature in Celsius

Output:
float — Temperature in Fahrenheit (rounded to 2 decimal places)

Constraints:

-100 <= C <= 100

Sample Input:

Expected Output:

77.00

2. 📐 Area of a Rectangle

Description:
Calculate the area of a rectangle using the formula:

Area = Length × Breadth

Input:
int L, B — Length and Breadth of the rectangle

Output:
int — Area of the rectangle

Constraints:

1 <= L, B <= 10^4

Sample Input:

15 10

Expected Output:

3. 🚗 Distance Covered by a Vehicle

Description:
Calculate the distance covered using the formula:

Distance = Speed × Time

Input:
int speed, int time

Output:
int — Total distance in km

Constraints:

1 <= speed <= 300
1 <= time <= 24

Sample Input:

60 5

Expected Output:

4. 🏗️ Number of Rounds of Lift

Description:
Given the total number of people P and lift capacity C, calculate the minimum number of rounds the lift needs to make to carry all people.

Input:
int P, int C

Output:
int — Minimum number of rounds required

Constraints:

1 <= P <= 10^5
1 <= C <= 100

Sample Input:

27 8

Expected Output:

Explanation:
8 + 8 + 8 + 3 → 4 rounds

5. 📈 Line Equation (y = mx + c)

Description:
Given values of m, x, and c, compute the value of y using:

y = m * x + c

Input:
int m, x, c

Output:
int — Computed value of y

Constraints:

-10^3 <= m, x, c <= 10^3

Sample Input:

2 4 3

Expected Output:

In-built Data Structure Practice Questions

Title
Problem Statement
Input Format
Output Format
Constraints
Sample Input/Output
Expected Output

1. ✅ Sum of List Elements

Description:
Calculate the sum of all elements in a list.

Input:
List[int] nums

Output:
int — Sum of elements

Constraints:

1 <= len(nums) <= 10^4
-10^6 <= nums[i] <= 10^6

Sample Input:
[1, 2, 3, 4, 5]

Expected Output:
15

2. ✅ Largest Element in a List

Description:
Return the largest number in the list.

Input:
List[int] nums

Output:
int — Maximum element

Constraints:

1 <= len(nums) <= 10^4

Sample Input:
[4, 17, 9, 1]

Expected Output:
17

3. ✅ Remove Duplicates in a List

Description:
Remove all duplicate values from a list while preserving order.

Input:
List[int] nums

Output:
List[int] — List without duplicates

Constraints:

1 <= len(nums) <= 10^4

Sample Input:
[1, 2, 2, 3, 1]

Expected Output:
[1, 2, 3]

4. ✅ Check if All Elements in a List are Unique

Description:
Check if a list contains all unique values.

Input:
List[int] nums

Output:
bool — True if all elements are unique, else False

Constraints:

1 <= len(nums) <= 10^5

Sample Input:
[1, 2, 3, 4]

Expected Output:
True

5. ✅ Program to Reverse a List

Description:
Return the reversed list.

Input:
List[Any] items

Output:
List[Any] — Reversed list

Sample Input:
[1, 2, 3, 4]

Expected Output:
[4, 3, 2, 1]

6. ✅ Count Number of Odd and Even Elements in a List

Description:
Count and return how many elements are odd and how many are even.

Input:
List[int] nums

Output:
Tuple[int, int] — (odd_count, even_count)

Sample Input:
[1, 2, 3, 4, 5]

Expected Output:
(3, 2)

7. ✅ Maximum Difference Between Two Consecutive Elements

Description:
Find the max absolute difference between any two consecutive elements.

Input:
List[int] nums

Output:
int

Sample Input:
[2, 9, 4, 1, 7]

Expected Output:
7

8. ✅ Merge Two Sorted Lists

Description:
Merge two sorted lists into a single sorted list.

Input:
List[int] list1, List[int] list2

Output:
List[int] — Sorted merged list

Sample Input:
[1, 3, 5], [2, 4, 6]

Expected Output:
[1, 2, 3, 4, 5, 6]

9. ✅ Rotate a List

Description:
Rotate the list k times to the right.

Input:
List[int] nums, int k

Output:
List[int]

Sample Input:
[1, 2, 3, 4, 5], k = 2

Expected Output:
[4, 5, 1, 2, 3]

10. ✅ Merge 2 Lists into Dictionary

Description:
Given two lists of equal length, create a dictionary with keys from first and values from second.

Input:
List[str] keys, List[Any] values

Output:
Dict[str, Any]

Sample Input:
['a', 'b', 'c'], [1, 2, 3]

Expected Output:
{'a': 1, 'b': 2, 'c': 3}

11. ✅ Merge Multiple Dictionaries

Description:
Merge all provided dictionaries into one. Later keys overwrite earlier ones.

Input:
List[Dict] dicts

Output:
Dict — Merged dictionary

Sample Input:
[{'a': 1}, {'b': 2}, {'a': 3}]

Expected Output:
{'a': 3, 'b': 2}

12. ✅ Word Frequency in a Sentence

Description:
Count frequency of each word in a given string.

Input:
str sentence

Output:
Dict[str, int]

Sample Input:
"this is a test this is"

Expected Output:
{'this': 2, 'is': 2, 'a': 1, 'test': 1}

13. ✅ Palindromic Tuple

Description:
Given a tuple of strings, return only palindromic elements.

Input:
Tuple[str] items

Output:
List[str] — Palindromes only

Sample Input:
('madam', 'racecar', 'hello')

Expected Output:
['madam', 'racecar']

14. ✅ Merge Dictionaries with Common Keys

Description:
Merge dictionaries by summing values of common keys.

Input:
List[Dict[str, int]] dicts

Output:
Dict[str, int]

Sample Input:
[{'a': 1, 'b': 2}, {'a': 3, 'c': 4}]

Expected Output:
{'a': 4, 'b': 2, 'c': 4}

15. ✅ Check if List is Subset of Another List

Description:
Return True if all elements of list A exist in list B.

Input:
List[int] A, List[int] B

Output:
bool

Sample Input:
[1, 2], [1, 2, 3, 4]

Expected Output:
True

Mathematical Practice Questions

1. ✅ Sum of N Even Natural Numbers

Description:
Calculate the sum of the first N even natural numbers.

Input:
int N

Output:
int — Sum of the first N even numbers

Constraints:

1 <= N <= 10^5

Sample Input:
5

Expected Output:
30

Explanation: Even numbers = 2 + 4 + 6 + 8 + 10 = 30

2. ✅ Check for Even Number

Description:
Check if a number is even.

Input:
int num

Output:
bool — True if even, else False

Constraints:

-10^9 <= num <= 10^9

Sample Input:
7

Expected Output:
False

3. ✅ Check for Prime Number

Description:
Check whether a number is prime.

Input:
int num

Output:
bool — True if prime, else False

Constraints:

0 <= num <= 10^6

Sample Input:
13

Expected Output:
True

4. ✅ Valid Perfect Square

Description:
Determine whether a number is a perfect square.

Input:
int num

Output:
bool — True if perfect square, else False

Constraints:

0 <= num <= 10^10

Sample Input:
36

Expected Output:
True

5. ✅ Decimal to Binary

Description:
Convert a non-negative integer to binary (without using built-in bin()).

Input:
int num

Output:
str — Binary representation

Constraints:

0 <= num <= 10^9

Sample Input:
10

Expected Output:
1010

6. ✅ Binary to Decimal

Description:
Convert a binary string to its decimal equivalent.

Input:
str binary

Output:
int — Decimal representation

Constraints:

1 <= len(binary) <= 32
Binary contains only '0' or '1'

Sample Input:
"1010"

Expected Output:
10

7. ✅ GCD of Two Numbers

Description:
Find the Greatest Common Divisor (GCD) of two numbers.

Input:
int a, int b

Output:
int — GCD of a and b

Constraints:

1 <= a, b <= 10^9

Sample Input:
20 28

Expected Output:
4

String Practice Questions

1. 🔁 Reverse a String

Description:
Reverse the characters of the given string.

Input:
str s

Output:
str — Reversed string

Constraints:

1 <= len(s) <= 10^5

Sample Input:
"hello"

Expected Output:
"olleh"

2. 🔡 Count Vowels in a String

Description:
Count the number of vowels (a, e, i, o, u) in the string.

Input:
str s

Output:
int — Number of vowels

Constraints:

1 <= len(s) <= 10^5

Sample Input:
"education"

Expected Output:
5

3. 🔍 Check for Same Strings

Description:
Return True if two strings are exactly the same, case-sensitive.

Input:
str s1, str s2

Output:
bool

Constraints:

1 <= len(s1), len(s2) <= 10^5

Sample Input:
"OpenAI", "OpenAI"

Expected Output:
True

4. 🔄 Check Palindrome

Description:
Check whether the given string is a palindrome (reads the same backward).

Input:
str s

Output:
bool

Constraints:

1 <= len(s) <= 10^5

Sample Input:
"racecar"

Expected Output:
True

5. 📝 Count Words in a String

Description:
Return the number of words in a sentence (words separated by whitespace).

Input:
str sentence

Output:
int

Constraints:

1 <= len(sentence) <= 10^5

Sample Input:
"This is a test"

Expected Output:
4

6. 🔁 Remove Duplicates in a String

Description:
Return the string with all duplicate characters removed, preserving the first occurrence.

Input:
str s

Output:
str

Constraints:

1 <= len(s) <= 10^5

Sample Input:
"banana"

Expected Output:
"ban"

7. 🧮 Count Consonants in a String

Description:
Return the number of consonants in the given string. Ignore spaces and vowels.

Input:
str s

Output:
int

Constraints:

1 <= len(s) <= 10^5

Sample Input:
"hello world"

Expected Output:
7

8. 🔄 Check for Anagrams

Description:
Check if two strings are anagrams (same characters, different order).

Input:
str s1, str s2

Output:
bool

Constraints:

1 <= len(s1), len(s2) <= 10^5

Sample Input:
"listen", "silent"

Expected Output:
True

9. ✅ Check Subsequence

Description:
Check if s1 is a subsequence of s2.

Input:
str s1, str s2

Output:
bool

Constraints:

1 <= len(s1), len(s2) <= 10^5

Sample Input:
"abc", "aebdc"

Expected Output:
True

10. 🔎 Check for Substring

Description:
Check if one string is a substring of another.

Input:
str small, str large

Output:
bool

Constraints:

1 <= len(small), len(large) <= 10^5

Sample Input:
"test", "this is a test string"

Expected Output:
True

11. 📏 Length of the Longest Word

Description:
Return the length of the longest word in a sentence.

Input:
str sentence

Output:
int

Constraints:

1 <= len(sentence) <= 10^5

Sample Input:
"The quick brown fox jumps"

Expected Output:
5
(“quick” or “jumps”)

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