1960.Maximum Product of the Length of Two Palindromic Substrings
HardHash FunctionRolling HashString32.1% acceptanceVideo
With video · 3,856 results
1961.Check If String Is a Prefix of Array
EasyArrayStringTwo Pointers52.7% acceptance1 companyVideo
1962.Remove Stones to Minimize the Total
MediumArrayGreedyHeap (Priority Queue)66.2% acceptance5 companiesVideo
1963.Minimum Number of Swaps to Make the String Balanced
MediumGreedyStackString78.0% acceptance12 companiesVideo
1964.Find the Longest Valid Obstacle Course at Each Position
HardArrayBinary Indexed TreeBinary Search62.8% acceptance1 companyVideo
1965.Employees With Missing Information
EasyDatabase73.7% acceptanceVideo
1966.Binary Searchable Numbers in an Unsorted Array
MediumArrayBinary Search63.3% acceptance3 companiesPremium elsewhere, free hereVideo
1967.Number of Strings That Appear as Substrings in Word
EasyArrayString86.1% acceptance6 companiesVideo
1968.Array With Elements Not Equal to Average of Neighbors
MediumArrayGreedySorting50.9% acceptance1 companyVideo
1969.Minimum Non-Zero Product of the Array Elements
MediumGreedyMathRecursion37.5% acceptance2 companiesVideo
1970.Last Day Where You Can Still Cross
HardArrayBinary SearchBreadth-First Search68.7% acceptance4 companiesVideo
1971.Find if Path Exists in Graph
EasyBreadth-First SearchDepth-First SearchGraph55.5% acceptance5 companiesVideo
1972.First and Last Call On the Same Day
HardDatabase50.7% acceptance1 companyPremium elsewhere, free hereVideo
1973.Count Nodes Equal to Sum of Descendants
MediumBinary TreeDepth-First SearchTree77.4% acceptance1 companyPremium elsewhere, free hereVideo
1974.Minimum Time to Type Word Using Special Typewriter
EasyGreedyString79.1% acceptance3 companiesVideo
1975.Maximum Matrix Sum
MediumArrayGreedyMatrix67.6% acceptance6 companiesVideo
1976.Number of Ways to Arrive at Destination
MediumDynamic ProgrammingGraphShortest Path37.4% acceptance5 companiesVideo
1977.Number of Ways to Separate Numbers
HardDynamic ProgrammingStringSuffix Array21.7% acceptance1 companyVideo
1978.Employees Whose Manager Left the Company
EasyDatabase48.9% acceptance4 companiesVideo
1979.Find Greatest Common Divisor of Array
EasyArrayMathNumber Theory83.4% acceptance5 companiesVideo
1980.Find Unique Binary String
MediumArrayBacktrackingHash Table81.2% acceptance5 companiesVideo
1981.Minimize the Difference Between Target and Chosen Elements
MediumArrayDynamic ProgrammingMatrix36.8% acceptance2 companiesVideo
1982.Find Array Given Subset Sums
HardArrayDivide and Conquer49.7% acceptance1 companyVideo
1983.Widest Pair of Indices With Equal Range Sum
MediumArrayHash TablePrefix Sum54.0% acceptance1 companyPremium elsewhere, free hereVideo
1984.Minimum Difference Between Highest and Lowest of K Scores
EasyArraySliding WindowSorting66.2% acceptance5 companiesVideo
1985.Find the Kth Largest Integer in the Array
MediumArrayDivide and ConquerHeap (Priority Queue)48.3% acceptance1 companyVideo
1986.Minimum Number of Work Sessions to Finish the Tasks
MediumArrayBacktrackingBit Manipulation35.3% acceptance2 companiesVideo
1987.Number of Unique Good Subsequences
HardDynamic ProgrammingString52.7% acceptance2 companiesVideo
1988.Find Cutoff Score for Each School
MediumDatabase66.8% acceptancePremium elsewhere, free hereVideo
1989.Maximum Number of People That Can Be Caught in Tag
MediumArrayGreedy49.4% acceptancePremium elsewhere, free hereVideo
1990.Count the Number of Experiments
MediumDatabase49.1% acceptance1 companyPremium elsewhere, free hereVideo
1991.Find the Middle Index in Array
EasyArrayPrefix Sum70.5% acceptance4 companiesVideo
1992.Find All Groups of Farmland
MediumArrayBreadth-First SearchDepth-First Search75.6% acceptance2 companiesVideo
1993.Operations on Tree
MediumArrayBreadth-First SearchDepth-First Search46.3% acceptance3 companiesVideo
1994.The Number of Good Subsets
HardArrayBit ManipulationBitmask37.8% acceptance2 companiesVideo
1995.Count Special Quadruplets
EasyArrayEnumerationHash Table65.1% acceptance3 companiesVideo
1996.The Number of Weak Characters in the Game
MediumArrayGreedyMonotonic Stack44.7% acceptance1 companyVideo
1997.First Day Where You Have Been in All the Rooms
MediumArrayDynamic Programming40.5% acceptance1 companyVideo
1998.GCD Sort of an Array
HardArrayMathNumber Theory51.3% acceptance1 companyVideo
1999.Smallest Greater Multiple Made of Two Digits
MediumEnumerationMath47.4% acceptance1 companyPremium elsewhere, free hereVideo
2000.Reverse Prefix of Word
EasyStackStringTwo Pointers86.3% acceptance5 companiesVideo
2001.Number of Pairs of Interchangeable Rectangles
MediumArrayCountingHash Table53.1% acceptance2 companiesVideo
2002.Maximum Product of the Length of Two Palindromic Subsequences
MediumBacktrackingBit ManipulationBitmask63.0% acceptance2 companiesVideo
2003.Smallest Missing Genetic Value in Each Subtree
HardDepth-First SearchDynamic ProgrammingTree48.4% acceptanceVideo
2004.The Number of Seniors and Juniors to Join the Company
HardDatabase46.6% acceptancePremium elsewhere, free hereVideo
2006.Count Number of Pairs With Absolute Difference K
EasyArrayCountingHash Table85.4% acceptance4 companiesVideo
2007.Find Original Array From Doubled Array
MediumArrayGreedyHash Table41.0% acceptance6 companiesVideo
2008.Maximum Earnings From Taxi
MediumArrayBinary SearchDynamic Programming46.9% acceptance8 companiesVideo
2009.Minimum Number of Operations to Make Array Continuous
HardArrayBinary SearchHash Table52.0% acceptance5 companiesVideo
2010.The Number of Seniors and Juniors to Join the Company II
HardDatabase66.2% acceptancePremium elsewhere, free hereVideo
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How to use these solutions
Each solution breaks the problem into approaches, usually from brute force to the best one, and explains why each works. Code comes in Python, Java, C++ and other languages. Knowing why an approach works matters more in an interview than remembering the code.
- Try the problem first. Give it at least 20 minutes before you open the solution.
- Read every approach. The brute force shows you the problem; the faster ones show the pattern.
- Check the complexity. Note the time and space of each approach and what makes the difference.
- Write it yourself. Close the solution and code it from memory in the editor.
- Come back in a week. Solving it again later is what makes the pattern stick.