Two Sumeasy0/3 skills readyTwo-sum with a value-to-index mapCheck whether a map contains a keyGet the value for a keyopen
Group Anagramsmedium0/3 skills readyGroup values by a keyAppend to a list under a keyBuild a frequency mapopen
Contains Duplicateeasy0/3 skills readyDetect a duplicate with a seen-setInsert one value into a setReturn early on a set hitopen
Intersection of Two Arrayseasy0/2 skills readyFind common values with a setHash the smaller collectionopen
Best Time to Buy and Sell Stockeasy0/3 skills readyKeep best-so-farMaintain running min/maxCompare with historical stateopen
Rotate Arraymedium0/3 skills readyRotate right by kNormalize with moduloHandle k greater than lengthopen
Valid Palindromeeasy0/3 skills readyPlace opposite-end pointersSkip non-alphanumeric charactersConvert a character to lowercaseopen
Two Sum IImedium0/3 skills readyTarget-sum with opposite pointersRequire sorted order before facing pointersMove left when the pair sum is too smallopen
Maximum Average Subarray Ieasy0/3 skills readyFix the window length in advanceSlide by dropping left and adding rightMaintain the sum of the windowopen
Longest Substring Without Repeating Charactersmedium0/3 skills readyUnique-character window shrinks on a repeatMaintain distinct count in the windowTrack the best valid lengthopen
Product of Array Except Selfmedium0/3 skills readyExclude current elementCombine prefix and suffixBuild suffix productsopen
Container With Most Watermedium0/3 skills readyClose the gap from both endsDecide which end to advanceCompare values at both endsopen
Max Consecutive Ones IIImedium0/3 skills readyAt most k zeros in the windowShrink while the window is invalidLongest valid window expands greedilyopen