Code Challenges

Get better at coding with practice problems.

Coding Challenges

Select a problem, write code, run test cases, and submit your solution.

Array Hash Map Counting

Learner

Implement the `containsDuplicateWithinK` method that checks whether duplicate values appear within distance k.

Array Hash Map Counting

Intermediate

Implement the `subarraySumEqualsKCount` method that counts subarrays whose sum equals k.

Array Hash Map Counting

Intermediate

Implement the `longestConsecutiveSequenceLength` method that returns the length of the longest consecutive number sequence.

Array Hash Map Counting

Learner

Implement the `twoSumUsingMap` method that returns two indices that form the target sum using a hash map.

String Manipulation String Hash Map Counting Character Pattern Matching

Learner

Implement the `romanNumeralToInteger` method that converts a Roman numeral string into an integer.

String Manipulation String Hash Map Counting Character Pattern Matching

Learner

Implement the `checkStringRotation` method that checks whether one string is a rotation of another string.

String Manipulation String Hash Map Counting Character Pattern Matching

Learner

Implement the `firstUniqueCharacterIndex` method that returns the index of the first character that appears only once.

String Manipulation String Hash Map Counting Character Pattern Matching

Proficient

Implement the `minimumWindowContainsPatternLength` method that returns the length of the smallest substring containing all pattern characters.

String Manipulation String Hash Map Counting Character Pattern Matching

Intermediate

Implement the `stringCompressionLength` method that returns the length after compressing consecutive repeated characters.

String Manipulation String Hash Map Counting Character Pattern Matching

Learner

Implement the `validPalindromeAlphanumeric` method that checks whether a text is a palindrome after ignoring non-alphanumeric characters.

String Manipulation String Hash Map Counting Character Pattern Matching

Intermediate

Implement the `longestPalindromicSubstringLength` method that returns the length of the longest palindromic substring.

String Manipulation String Hash Map Counting Character Pattern Matching

Intermediate

Implement the `groupAnagramCount` method that counts how many anagram groups are formed from the words.

String Manipulation String Hash Map Counting Character Pattern Matching

Learner

Implement the `validAnagramCheck` method that checks whether two strings are anagrams.

String Manipulation String Hash Map Counting Character Pattern Matching

Intermediate

Implement the `longestSubstringNoRepeat` method that returns the length of the longest substring without repeated characters.

Loop Array Hash Map Counting Prefix Sum

Intermediate

Implement the `nextPermutationRankChange` method that returns the next lexicographical permutation of the array.

Loop Array Hash Map Counting Prefix Sum

Learner

Implement the `maximumConsecutiveOnes` method that returns the longest run of consecutive 1 values.

Loop Array Hash Map Counting Prefix Sum

Intermediate

Implement the `mergeOverlappingIntervalsCount` method that returns how many intervals remain after merging all overlaps.

Loop Array Hash Map Counting Prefix Sum

Learner

Implement the `missingNumberZeroToN` method that finds the missing number from the range 0 to n.

Loop Array Hash Map Counting Prefix Sum

Learner

Implement the `findDuplicateNumber` method that returns a duplicate value from the array.