Question

How to count the total of all pairs permutations in an array with JavaScript

Answer 1

const arr1 = [1, 8, 5];

// The pairs are: (1, 8), (1, 5), (8, 1), (8, 5), (5, 1), (5, 8)

let total_pairs = arr1.length * (arr1.length - 1);
console.log("Total Pairs = " + total_pairs);

const arr2 = [1, 8, 5, 2];

// The pairs are: (1, 8), (1, 5), (1, 2), (8, 1), (8, 5), (8, 2),
//                (5, 1), (5, 8), (5, 2), (2, 1), (2, 8), (2, 5)

total_pairs = arr2.length * (arr2.length - 1);
console.log("Total Pairs = " + total_pairs);



/*
run:

Total Pairs = 6
Total Pairs = 12

*/

 

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