Count Good Triplets in an Array — Algorithm Visualization & Coding Challenge

Choose Your Learning Path

How would you like to learn today?
Visualize algorithms in real time, explore them step by step, or challenge yourself with a test.Choose a path to focus—or scroll down to preview all options.

🧠 Active Learning

Visualize the algorithm step-by-step with interactive animations in real time.

📖 Passive Learning

Read the full explanation, examples, and starter code at your own pace.

🎯 Challenge Mode

Drag and arrange the algorithm steps in the correct execution order.

🧠 Select Active to activate

JUMP INTO VISUALIZATION

Watch algorithms run step by step.

Follow every state change, comparison, and transformation as the execution unfolds in real time.

📖 Select Passive to activate

Understanding Count Good Triplets in an Array

Detailed explanation and reference materials

Problem Overview

Count Good Triplets in an Array

Difficulty: Hard

Topics:
Array , Binary Search , Binary Indexed Tree , Divide and Conquer , Merge Sort , Ordered Set , Segment Tree

Hint:
You are given two 0-indexed arrays nums1 and nums2 of length n, both of which are permutations of [0, 1, ..., n - 1].

A good triplet is a set of 3 distinct values which are present in increasing order by position both in nums1 and nums2. In other words, if we consider pos1v as the index of the value v in nums1 and pos2v as the index of the value v in nums2, then a good triplet will be a set (x, y, z) where 0 <= x, y, z <= n - 1, such that pos1x < pos1y < pos1z and pos2x < pos2y < pos2z.

Return the total number of good triplets.

Example 1

Input: nums1 = [2,0,1,3], nums2 = [0,1,2,3] Output: 1 Explanation: There are 4 triplets (x, y, z) such that pos1x < pos1y < pos1z. They are (2,0,1), (2,0,3), (2,1,3), and (0,1,3). Out of those triplets, only the triplet (0,1,3) satisfies pos2x < pos2y < pos2z. Hence, there is only 1 good triplet.

Example 2

Input: nums1 = [4,0,1,3,2], nums2 = [4,1,0,2,3] Output: 4 Explanation: The 4 good triplets are (4,0,3), (4,0,2), (4,1,3), and (4,1,2).

Constraints

$n = \text{nums1.length} = \text{nums2.length}$
$3 \le n \le 10^5$
$0 \le \text{nums1}[i], \ \text{nums2}[i] \le n - 1$
$\text{nums1 and nums2 are permutations of } \{ 0, 1, \dots, n - 1 \}$

— Written by Saurabh Patil • B.Tech CSE • Software Developer

Reference Link

https://leetcode.com/problems/count-good-triplets-in-an-array/

Loading component...

Starter Code

Test, modify, or copy the starter code. Click "Visualize" to import into the canvas.

Java

Output:

Understood Algorithm, Test Me now 🎮

🎯 Select Challenge to activate

🧠 Logic Puzzle

Think & Arrange, Don't Just Copy-Paste

Drag and arrange the algorithm steps in the correct execution order instead of spending time typing code letter by letter.

Arrange the Algorithm Correctly 🧩

The algorithm is divided into three logical parts. Carefully rearrange each section in the correct order to form a complete and valid solution.

Understand Below Algorithm

Green text means the instruction is placed in the correct position.

Red text means the instruction is in the wrong position.

Block Colors

Instructions with the same background color indicate particular blocks start and end.

A tick mark means the instruction is correct and locked.

🔒 Locked steps cannot be moved. Only unlocked steps are draggable.

🔊 Enable sound for swap feedback and completion effects.