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0202-happy-number.js
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0202-happy-number.js
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// 202. Happy Number
// Easy 40%
// Write an algorithm to determine if a number is "happy".
// A happy number is a number defined by the following process: Starting with any
// positive integer, replace the number by the sum of the squares of its digits,
// and repeat the process until the number equals 1 (where it will stay), or it
// loops endlessly in a cycle which does not include 1. Those numbers for which
// this process ends in 1 are happy numbers.
// Example: 19 is a happy number
// 1^2 + 9^2 = 82
// 8^2 + 2^2 = 68
// 6^2 + 8^2 = 100
// 1^2 + 0^2 + 0^2 = 1
// Credits:Special thanks to @mithmatt and @ts for adding this problem and
// creating all test cases.
/**
* @param {number} n
* @return {boolean}
*/
const isHappy = function(n) {
const hash = {}
while (hash[n] == null) {
hash[n] = true
let sum = 0
while (n > 0) {
sum += Math.pow(n % 10, 2)
n = Math.trunc(n / 10)
}
if (sum === 1) return true
n = sum
}
return false
}
;[
19, // true
7, // true
2, // false
].forEach(n => {
console.log(isHappy(n))
})
// Solution:
// 用哈希保存出现过的数字,若再次出现则会循环,返回 false
// 否则继续计算,直达算出 1 。
// Submission Result: Accepted