Complete Beginner Roadmap
Master the core programming skills needed for success in college coursework and personal projects
Programming Fundamentals for College & Side Projects
Focus on for-loops, arrays, and conditional logic - the building blocks of all programming.
Practice Environment
Use LeetCode Playground or your local IDE to write functions that accept parameters and test your solutions.
Get Help When Stuck
Use an LLM (like ChatGPT/Claude) to help with input parsing if needed, but focus on the core logic.
Core Skills Focus
For-loops, arrays, conditionals - the most important skills for college and side projects.
What Matters Most
Input parsing is less important - focus on problem-solving logic and algorithm thinking.
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Fundamental Problems
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Beginner Level
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Key Concepts
Unsupported Type
Given a list of integers `arr` and a target integer `x`, check if `x` appears anywhere in `arr`. Return 'Yes' if found, 'No' if not. For example, if arr = [3, 1, 4] and x = 4, return 'Yes' because 4 is in the list.
Key Concepts:
Streamer Takahashi
A streamer broadcasts from hour `stream_start` to hour `stream_end`. Each listener has a time window [start, end] they can watch. Count how many listeners can watch the entire stream (their start <= stream_start AND their end >= stream_end).
Key Concepts:
Content Too Large
Given a list of item sizes and a bag's maximum capacity, check if the total size of all items fits in the bag. Return 'Yes' if the sum of items <= bag_size, 'No' otherwise.
Key Concepts:
Task Failed Successfully
Given two lists of equal length — `goals` (planned tasks per day) and `actual` (tasks completed per day) — count how many days Takahashi completed strictly more tasks than his goal. For example, goal=2 and actual=8 counts as exceeded.
Key Concepts:
Required Length
Given a password string and a minimum required length, check if the password has at least that many characters. Return 'Yes' if len(password) >= min_length, 'No' otherwise.
Key Concepts:
G1
Given a list of age limits for horse races and a horse's age `k`, count how many races the horse can enter. A horse can enter a race if its age is less than or equal to the race's age limit (k <= ages[i]).
Key Concepts:
Conflict
Takahashi and Aoki each want certain items. Their preferences are given as strings of 'o' (wants) and 'x' (doesn't want). Check if there's any position where both have 'o' — meaning they both want the same item. Return 'Yes' if a conflict exists, 'No' otherwise.
Key Concepts:
Timeout
An elder starts awake at time 0 and is tapped at times given in `taps`. The elder falls asleep if more than `s` seconds pass between consecutive taps (or from time 0 to the first tap). Return 'Yes' if the elder stays awake through all taps, 'No' if they ever fall asleep.
Key Concepts:
Approximation
Given two positive integers `a` and `b`, find the integer closest to a / b. For example, 4 / 7 ≈ 0.57, so the closest integer is 1. Use standard rounding (round half away from zero since b is always odd).
Key Concepts:
Not Acceptable
Check if a submission time (C:D) is strictly before a deadline (A:B), where times are in hours and minutes. Return 'Yes' if submitted before the deadline, 'No' otherwise. Compare hours first, then minutes.
Key Concepts:
Is it rated?
Check if a contestant's rating is 'rated' in a given division. Division 1 is rated for ratings 1600–2999. Division 2 is rated for ratings 1200–2399. Return 'Yes' if the rating falls in the range for the given division, 'No' otherwise.
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Not Found
Given a string of lowercase English letters, find and return one letter (a-z) that does NOT appear in the string. Any missing letter is a valid answer.
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Odd Position Sum
Given a list of integers, calculate the sum of elements at odd positions (1st, 3rd, 5th, etc. using 1-based indexing). For example, in [3, 1, 4, 1, 5], the elements at positions 1, 3, 5 are 3, 4, 5, so the sum is 12.
Key Concepts:
CBC
Given a string containing both uppercase and lowercase letters, extract only the uppercase letters and return them as a new string in their original order. For example, 'AtCoderBeginnerContest' → 'ACBC'.
Key Concepts:
Status Code
Given an HTTP status code (integer between 100–999), return 'Success' if it's between 200 and 299 (inclusive), or 'Failure' otherwise.
Key Concepts:
ABC400 Party
400 people need to sit in a rectangle with `a` rows. Calculate how many columns `b` are needed so that a × b = 400. If 400 is not divisible by a, return -1.
Key Concepts:
Hamming Distance
Given two strings of equal length, count the number of positions where the characters differ. This is called the Hamming distance. For example, 'abcarc' vs 'agcahc' differ at positions 2 and 5, so the distance is 2.
Key Concepts:
Doors in the Center
Create a palindrome string of length `n` using only '-' and '=' characters. If n is odd, place exactly one '=' in the center. If n is even, place exactly two '=' in the center. Fill the rest with '-'. For example, n=5 → '--=--', n=4 → '-==-'.
Key Concepts:
Thermometer
Classify a body temperature: return 1 if temperature >= 38.0 (high fever), 2 if >= 37.5 but < 38.0 (fever), or 3 if < 37.5 (normal).
Key Concepts:
Triple Four
Given a list of integers, check if any value appears three or more times consecutively (in a row). Return 'Yes' if such a triple exists, 'No' otherwise. For example, [1, 4, 4, 4, 2] → 'Yes' because 4 appears three times in a row.
Key Concepts:
Strictly Increasing?
Check if a list of integers is strictly increasing — meaning each element is strictly less than the next one. Return 'Yes' if strictly increasing, 'No' otherwise. Note: equal consecutive values (like [1, 1, 2]) are NOT strictly increasing.
Key Concepts:
22222
Given a string of digits, remove every character that is not '2' and return the remaining string. For example, '20250222' → '22222'.
Key Concepts:
Poisonous Oyster
Two people ate different combinations of 4 oyster types. Person 1 ate types 1 and 2. Person 2 ate types 1 and 3. Exactly one type is poisonous. Based on whether each person felt 'sick' or 'fine', determine which oyster type (1, 2, 3, or 4) is poisonous.
Key Concepts:
Shuffled Equation
Given three integers a, b, c, check if any arrangement of them satisfies the equation: one number × another number = the third number. Return 'Yes' if possible, 'No' otherwise. For example, (3, 15, 5) → 'Yes' because 3 × 5 = 15.
Key Concepts:
Lucky Direction
Given a compass direction as a string (like 'N', 'SE', 'NW'), return the opposite direction. Swap N↔S and E↔W. For example, 'SE' → 'NW', 'N' → 'S'.
Key Concepts:
12435
Given a list of 5 integers (a permutation of 1-5), check if you can sort it in ascending order by swapping exactly one pair of adjacent elements. Return 'Yes' if exactly one adjacent swap produces [1,2,3,4,5], 'No' otherwise.
Key Concepts:
9x9
Given a string in the format 'AxB' where A and B are single digits (1-9), return their product A × B as an integer. For example, '3x8' → 24.
Key Concepts:
?UPC
Take the first character of the input string and append 'UPC' to it. Return the result. For example, 'Kyoto' → 'KUPC'.
Key Concepts:
Happy New Year 2025
Given two positive integers a and b, calculate (a + b)². Return the result. For example, square_of_sum(20, 25) = (20+25)² = 45² = 2025.
Key Concepts:
Full House 2
Given 4 card values, determine if adding exactly one more card can form a Full House (three of one value + two of another). Return 'Yes' if possible, 'No' otherwise. For example, [7,7,7,1] → 'Yes' (add another 1 to get 7,7,7,1,1).
Key Concepts:
Equally
Given three integers a, b, c, check if they can be split into two or more groups where each group has the same sum. For example, (3, 8, 5) → 'Yes' because {3,5} and {8} both sum to 8.
Key Concepts:
aaaadaa
Given a string `s`, a character to keep `c1`, and a replacement character `c2`, replace every character in s that is NOT c1 with c2. Return the modified string. For example, s='atcoder', c1='d', c2='a' → 'aaaadaa'.
Key Concepts:
Humidifier 1
A humidifier starts empty. Water is added at specific times (given as (time, volume) pairs). Between additions, water decreases by 1 unit per time unit (but never below 0). Calculate the water remaining after the last addition.
Key Concepts:
Daily Cookie
Given a string of boxes where '@' = cookie and '.' = empty, Takahashi eats one cookie per day for `d` days. Count how many boxes will be empty after d days. Empty boxes = original empty boxes + d cookies eaten.
Key Concepts:
11/22 String
Check if a string made of '1', '2', and '/' is an 11/22 string. Rules: odd length, the first half is all '1's, the exact middle character is '/', and the second half is all '2's. Return 'Yes' or 'No'. Example: '11/22' → 'Yes', '/' → 'Yes'.
Key Concepts:
123233
Check if a 6-digit number contains exactly one '1', exactly two '2's, and exactly three '3's (and no other digits). Return 'Yes' if it does, 'No' otherwise.
Key Concepts:
Cyclic
Given a 3-digit number with digits a, b, c, create two new numbers by cyclically rearranging: bca and cab. Return them as a space-separated string. For example, 379 → '793 937'.
Key Concepts:
Pairing
Given a list of 4 ball colors (as integers), find the maximum number of pairs you can form. A pair is two balls of the same color. For example, [2,1,2,1] → 2 pairs (one pair of 1s, one pair of 2s).
Key Concepts:
Rearranging ABC
Check if a 3-character string can be rearranged to spell 'ABC'. Return 'Yes' if it contains exactly one A, one B, and one C; 'No' otherwise.
Key Concepts:
Candy Button
A button is pressed at times given in list `t`. A candy is dispensed only if at least `c` seconds have passed since the last candy was given (first press always gives a candy). Count the total candies received.
Key Concepts:
Seats
Given a string of seats where '#' = occupied and '.' = empty, count how many times the pattern '#.#' appears — a person in seat i, empty seat i+1, and a person in seat i+2.
Key Concepts:
Takahashi san 2
Check if a string (lowercase English letters only) ends with the suffix 'san'. Return 'Yes' if the last 3 characters are 'san', 'No' otherwise.
Key Concepts:
September
Given a list of 12 words, count how many have a length equal to their position (1-indexed). The 1st word should have length 1, the 2nd length 2, etc. For example, 'september' at position 9 has length 9, so it counts.
Key Concepts:
delete .
Remove all dot characters ('.') from the input string and return the result. Only dots are removed; all other characters stay. For example, '.v.' → 'v'.
Key Concepts:
Jiro
Three brothers A, B, C have their ages compared in 3 pairs: A vs B, A vs C, B vs C. Each comparison is '<' (first is younger) or '>' (first is older). Determine which brother is the second oldest and return 'A', 'B', or 'C'.
Key Concepts:
Raise Both Hands
Snuke raises hands to signal: left hand only (L=1, R=0) → 'Yes' (wants takoyaki), right hand only (L=0, R=1) → 'No' (doesn't want it), both or neither → 'Invalid'.
Key Concepts:
369
Given two integers a and b, count how many integers x exist such that a, b, and x can be arranged to form an arithmetic sequence (equal spacing between consecutive terms). For example, a=5, b=7 → 3 values: x=3, x=6, or x=9.
Key Concepts:
Cut
Given a list of cards and an integer k, move the bottom k cards to the top of the stack. Return the new order as a space-separated string. For example, cards=[1,2,3,4,5], k=3 → '3 4 5 1 2'.
Key Concepts:
Shout Everyday
Takahashi sleeps from hour `a` to hour `b` (may wrap past midnight). Determine if he is awake at hour `c`. Return 'Yes' if awake (not during sleep hours), 'No' if asleep.
Key Concepts:
Election 2
In an election with `n` total voters, Takahashi has `t` votes and Aoki has `a` votes so far. Determine if the winner is already certain — meaning even if all remaining votes (n - t - a) go to the losing candidate, they still can't catch up. Return 'Yes' if decided, 'No' otherwise.
Key Concepts:
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