--- title: Mastering "Triplets with Sum in Range": An Efficient... description: Explains how to solve the 'Triplets with Sum in Range' interview problem efficiently in Java, moving from a naive O(n^3) brute-force approach to an optimal... canonical: https://daily.dev/posts/mastering-triplets-with-sum-in-range-an-efficient-java-approach-62tp1iw6r twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Mastering "Triplets with Sum in Range": An Efficient Java Approach | daily.dev og:description: Explains how to solve the 'Triplets with Sum in Range' interview problem efficiently in Java, moving from a naive O(n^3) brute-force approach to an optimal... og:url: https://daily.dev/posts/mastering-triplets-with-sum-in-range-an-efficient-java-approach-62tp1iw6r og:image: https://api.daily.dev/og/posts/62tp1iw6R.png og:image:alt: Mastering "Triplets with Sum in Range": An Efficient Java Approach og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Mastering "Triplets with Sum in Range": An Efficient Java Approach **[C\# Corner](https://daily.dev/sources/csharpcorner)** · 3 min read · 1 upvotes · 0 comments ## Summary Explains how to solve the 'Triplets with Sum in Range' interview problem efficiently in Java, moving from a naive O(n^3) brute-force approach to an optimal O(n^2) time, O(1) space solution using sorting and the two-pointer technique. Covers the range query transformation Count(l,r) = Count(sum<=r) - Count(sum<=l-1), a walkthrough of the two-pointer logic, the Java implementation, and a breakdown of each code segment's complexity. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How do you count triplets in an array whose sum falls within a given range [l, r] efficiently? Sort the array, then compute the count of triplets with sum <= r and subtract the count of triplets with sum <= l-1. Each count uses a two-pointer scan: for each fixed index i, move pointers j and k inward, adding (k-j) to the total whenever arr[i]+arr[j]+arr[k] <= val. This achieves O(n^2) time and O(1) auxiliary space, versus O(n^3) for brute force. _Developers prepping for algorithm-heavy interviews can find more optimization patterns like this on daily.dev._ ## Similar posts on daily.dev - [3 Sum Problem in DSA \(Example and Optimized Solution\)](https://daily.dev/posts/3-sum-problem-in-dsa-example-and-optimized-solution--67wpded8f) · C\# Corner · 0 upvotes · 0 comments - [MIT Complexity Theorist On Leetcode](https://daily.dev/posts/mit-complexity-theorist-on-leetcode-0hduqghca) · The Developing Dev · 0 upvotes · 0 comments - [The Subset Sum Problem Solved in Linear Time for Dense Enough Inputs](https://daily.dev/posts/the-subset-sum-problem-solved-in-linear-time-for-dense-enough-inputs-sjlhgprsn) · Towards Data Science · 0 upvotes · 0 comments - [Equalize All Prefix Sums](https://daily.dev/posts/equalize-all-prefix-sums-1vho3hqp8) · C\# Corner · 0 upvotes · 0 comments - [Medium](https://daily.dev/posts/medium-tjownsknq) · Medium · 0 upvotes · 0 comments --- Tags: [#java](https://daily.dev/tags/java), [#algorithms](https://daily.dev/tags/algorithms), [#data-structures](https://daily.dev/tags/data-structures), [#interview-questions](https://daily.dev/tags/interview-questions) [View this post on daily.dev](https://daily.dev/posts/mastering-triplets-with-sum-in-range-an-efficient-java-approach-62tp1iw6r) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Mastering \"Triplets with Sum in Range\": An Efficient Java Approach","url":"https://daily.dev/posts/mastering-triplets-with-sum-in-range-an-efficient-java-approach-62tp1iw6r","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/mastering-triplets-with-sum-in-range-an-efficient-java-approach-62tp1iw6r"},"datePublished":"2026-08-19T08:50:42.681Z","dateModified":"2026-09-13T21:34:39.389Z","description":"Explains how to solve the 'Triplets with Sum in Range' interview problem efficiently in Java, moving from a naive O(n^3) brute-force approach to an optimal...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/81f698b062e81502c45df6b257ae3843?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/81f698b062e81502c45df6b257ae3843?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"C# Corner","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"C# Corner","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/ada2d584df6241748fc4e71878dc70a3","url":"https://daily.dev/sources/csharpcorner"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/mastering-triplets-with-sum-in-range-an-efficient-java-approach-62tp1iw6r","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":1},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"java,algorithms,data-structures,interview-questions","timeRequired":"PT3M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"C# Corner","item":"https://daily.dev/sources/csharpcorner"},{"@type":"ListItem","position":3,"name":"Mastering \"Triplets with Sum in Range\": An Efficient Java Approach"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/mastering-triplets-with-sum-in-range-an-efficient-java-approach-62tp1iw6r#faq","mainEntity":[{"@type":"Question","name":"How do you count triplets in an array whose sum falls within a given range [l, r] efficiently?","acceptedAnswer":{"@type":"Answer","text":"Sort the array, then compute the count of triplets with sum <= r and subtract the count of triplets with sum <= l-1. Each count uses a two-pointer scan: for each fixed index i, move pointers j and k inward, adding (k-j) to the total whenever arr[i]+arr[j]+arr[k] <= val. This achieves O(n^2) time and O(1) auxiliary space, versus O(n^3) for brute force. Developers prepping for algorithm-heavy interviews can find more optimization patterns like this on daily.dev."}}]} ```