Python LeetCode – Basic Problem Set

This repository contains a few beginner-friendly LeetCode problems. These questions help build confidence with arrays, loops, and basic logic. Each problem is simple, clear, and great for improving problem-solving skills step-by-step.

1️⃣ 1431. Kids With the Greatest Number of Candies

• For each kid, check if giving them extra candies makes them have the most candies.

• Helps understand comparing values in an array.

• Returns a list of true/false based on who can reach the maximum.

2️⃣ 1480. Running Sum of 1D Array

• Calculates the running total of numbers from left to right.

• Helps practice loops and keeping track of a growing sum.

• Great for understanding how prefix sums work.

3️⃣ 1470. Shuffle the Array

• Mixes two halves of an array into an alternating pattern.

• Builds understanding of index handling and rearranging lists.

• Very useful for practicing basic array manipulation.

1️⃣ Number of Good Pairs

Step-by-step explanation

• You are given an array of integers called nums.

• You need to look at two different positions in the array at a time.

• For each pair of positions (i, j), check that i < j.

• Compare the values at those positions: nums[i] and nums[j].

• If both values are equal, then that pair is called a good pair.

• Count all such good pairs and return the total count.

2️⃣ Find Numbers with Even Number of Digits

Step-by-step explanation

• You are given a list (array) of integers.

• Take one number at a time from the list.

• Count how many digits that number contains.

• Check whether the digit count is an even number.

• Keep a running count of all numbers that have an even number of digits.

• After checking all the numbers, return the final count.

3️⃣ Number of Good Pairs

Step-by-step explanation

• You are given a list of integers.

• Pick one number and compare it with the numbers that come after it in the list.

• For each comparison, check whether both numbers are equal.

• Make sure the index of the first number is smaller than the index of the second number.

• If both conditions are satisfied, consider it a valid (good) pair.

• Count all such valid pairs and return the total count.

4️⃣ How Many Numbers Are Smaller Than the Current Number

Step-by-step explanation

• You are given a list of integers.

• Pick one number from the list.

• Compare this number with all other numbers in the list.

• Count how many numbers are smaller than the current number.

• Store this count in the result list at the same position.

• Repeat the process for every number and return the final list of counts.

5️⃣ Subtract the Product and Sum of Digits of an Integer

Step-by-step explanation

• You are given a single integer number.

• Break the number into its individual digits.

• Calculate the product of all the digits.

• Calculate the sum of all the digits.

• Subtract the sum of the digits from the product of the digits.

• Return the final result.

6️⃣ XOR Operation in an Array

Step-by-step explanation

• You are given two integers: n and start.

• Create an array with length n.

• For each index i, calculate the value using the formula start + 2 × i.

• Store each calculated value in the array.

• Apply the XOR operation between all the elements of the array.

• Return the final XOR result.

1️⃣ 1464. Maximum Product of Two Elements in an Array

• Difficulty: Easy

Problem Statement:

• Given an integer array nums, choose two different indices i and j and return the maximum value of (nums[i]−1)∗(nums[j]−1)

Core Idea:

• Identify the two largest elements in the array

• Subtract 1 from each

• Compute the product

Key Skills Demonstrated:

• Greedy selection

• Array scanning

• Optimization without sorting

2️⃣ 1395. Count Number of Teams

• Difficulty: Medium

Problem Statement:

• Given unique soldier ratings, count the number of valid teams of size 3 such that:

• Ratings are strictly increasing or

• Ratings are strictly decreasing with indices i < j < k.

Core Idea:

• Fix a middle soldier

• Count smaller and larger elements on both sides

• Combine counts to form valid triplets

Key Skills Demonstrated:

• Nested iteration with constraints

• Combinatorial counting

• Pattern recognition (increasing vs decreasing sequences)

3️⃣ 1450. Number of Students Doing Homework at a Given Time

• Difficulty: Easy

Problem Statement:

• Given startTime, endTime, and queryTime, return how many students are doing homework at queryTime.

Core Idea:

• Iterate through students

• Check if queryTime lies in the inclusive interval

Key Skills Demonstrated:

• Interval validation

• Linear scanning

• Condition-based counting

4️⃣ 1342. Number of Steps to Reduce a Number to Zero

• Difficulty: Easy

Problem Statement:

• Reduce a number to zero using:

• Divide by 2 if even

• Subtract 1 if odd

• Return the number of steps.

Core Idea:

• Repeatedly apply rules until the number becomes zero

• Maintain a step counter

Key Skills Demonstrated:

• Loop control

• Even/odd logic

• Simulation-based problem solving

5️⃣ 338. Counting Bits

• Difficulty: Easy

Problem Statement:

• For a given integer n, return an array where each index i contains the count of 1s in the binary representation of i.

Core Idea:

• Build results incrementally from 0 to n

• Leverage previous computations (dynamic programming)

Key Skills Demonstrated:

• Bit manipulation

• Dynamic programming mindset

• Binary number understanding

🛠️ Tech Stack

• Language: Python

• Paradigm: Iterative, Greedy, Dynamic Programming

Complexity Focus:

• Time: O(n), O(n²) where required

• Space: Optimized, minimal auxiliary usage

▶️ How to Use

• Pick any problem from the list.

• Read the short explanation.

• Check or write your solution inside the solutions/ folder.