LeetCode: Happy Number Solution

Approach

Cycle here means a number is processed for the second time

Implementation

1var isHappy = function (n) {
2  const set = new Set()
3
4  while (true) {
5    if (n === 1) break
6    if (set.has(n)) return false
7    set.add(n)
8
9    let sum = 0
10    while (n) {
11      const lastDigit = n % 10
12      sum += lastDigit * lastDigit
13      n = Math.floor(n / 10)
14    }
15    n = sum
16  }
17  return true
18}

Implementation (shorter)

Don't want to waste time on social media?

1var isHappy = function (n) {
2  const set = new Set()
3
4  while (!set.has(n)) {
5    set.add(n)
6    n = String(n)
7      .split("")
8      .reduce((acc, digit) => acc + digit * digit, 0)
9  }
10
11  return n === 1
12}

References

Original problem

Similar problems

Linked List Cycle

Add Digits

Ugly Number

Sum of Digits of String After Convert

Minimum Addition to Make Integer Beautiful