Happy Number

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Write an algorithm to determine if a number n is happy.

A happy number is defined by repeatedly replacing the number by the sum of the squares of its digits until it equals 1. If it loops endlessly in a cycle that does not include 1, then it is not happy.

Use a hash set to detect cycles.

Example 1:

Input: n = 19
Output: true

Example 2:

Input: n = 2
Output: false

Example 3:

Input: n = 1
Output: true

Algorithm Flow

Recommendation Algorithm Flow for Happy Number - Budibadu

Best Answers

java

import java.util.*;
class Solution {
    public boolean happy_number(int n) {
        Set<Integer> seen = new HashSet<>();
        while (n != 1 && !seen.contains(n)) {
            seen.add(n);
            int total = 0;
            while (n > 0) {
                int d = n % 10;
                total += d * d;
                n /= 10;
            }
            n = total;
        }
        return n == 1;
    }
}

javascript

function happy_number(n) {
    function nextNum(x) {
        let total = 0;
        while (x > 0) {
            const d = x % 10;
            total += d * d;
            x = Math.floor(x / 10);
        }
        return total;
    }
    const seen = {};
    while (n !== 1 && !seen[n]) {
        seen[n] = true;
        n = nextNum(n);
    }
    return n === 1;
}

php

<?php
function happy_number($n) {
    $seen = [];
    while ($n != 1 && !isset($seen[(string)$n])) {
        $seen[(string)$n] = true;
        $sum = 0;
        while ($n > 0) {
            $d = $n % 10;
            $sum += $d * $d;
            $n = intdiv($n, 10);
        }
        $n = $sum;
    }
    return $n == 1;
}
?>

python

def happy_number(n: int) -> bool:
    def next_num(x: int) -> int:
        total = 0
        while x > 0:
            d = x % 10
            total += d * d
            x //= 10
        return total
    seen = set()
    while n != 1 and n not in seen:
        seen.add(n)
        n = next_num(n)
    return n == 1

rust

use std::collections::HashSet;
fn happy_number(mut n: i32) -> bool {
    let mut seen: HashSet<i32> = HashSet::new();
    while n != 1 && !seen.contains(&n) {
        seen.insert(n);
        let mut x = n;
        let mut sum = 0;
        while x > 0 {
            let d = x % 10;
            sum += d * d;
            x /= 10;
        }
        n = sum;
    }
    n == 1
}

typescript

function happy_number(n: number): boolean {
    function nextNum(x: number): number {
        var total = 0;
        while (x > 0) {
            var d = x % 10;
            total += d * d;
            x = Math.floor(x / 10);
        }
        return total;
    }
    var seen: { [key: string]: boolean } = {};
    while (n !== 1 && !seen[String(n)]) {
        seen[String(n)] = true;
        n = nextNum(n);
    }
    return n === 1;
}

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Happy Number

Algorithm Flow

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