# Sap Community Coding Challenge nr. 2 - solution

node v8.17.0
version: 3.0.0
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I would say it is node.js task since there was nothing about presentation in requirements. Rather simple... ;)
/* Every given number have one postion on calculated sequence, that is constant, for all posible sequences, therefore it can be reused. */ let positions = {} const isOdd = x => x & 1 const nextN = n => isOdd(n) ? 3 * n + 1 : n / 2 const calculateSequence = n => { let sequence = [n] do { n = nextN(n) sequence.push(n) // If n positioned already - not need to continue if (positions[n] !== undefined) { return sequence break } } while (n != 1) return sequence } const mapSequence = sequence => { let i = 1 for (var n of sequence.reverse()) { // Sequence is compleate and new if (n == 1) { positions[n] = i } else { // Number from sequence is positioned if (i == 1) { // So we just take already calculated position and continue i = positions[n] } else { positions[n] = i } } i++ } } const highestLengthFromCollatzConjecture = limit => { for (var j = limit; j > 0; j--) { let sequence = calculateSequence(j) mapSequence(sequence) } let highestLength = 0 let startingNumber = 1 for (var k = limit; k > 0; k--) { if (positions[k] > highestLength) { startingNumber = k highestLength = positions[k] } } return [startingNumber, highestLength] } const [startingNumber, highestLength] = highestLengthFromCollatzConjecture(1000000) console.log(`Starting Number: \${startingNumber} had highest length of \${highestLength}.`)