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:
Input: 19
Output: true
Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1
ไปฃ็
Approach #1 HashSet
classSolution {publicbooleanisHappy(int n) {Set<Integer> seen =newHashSet<>();while (n !=1&&!seen.contains(n)) {seen.add(n); n =getNext(n); }return n ==1; }privateintgetNext(int n) {int totalSum =0;while (n >0) {int d = n %10; n = n /10; totalSum += d * d; }return totalSum; }}
Approach #2 Floyd's Cycle-Finding Algorithm
classSolution {publicbooleanisHappy(int n) {int slowRunner = n;int fastRunner =getNext(n);while (fastRunner !=1&& slowRunner != fastRunner) { slowRunner =getNext(slowRunner); fastRunner =getNext(getNext(fastRunner)); }return fastRunner ==1; }privateintgetNext(int n) {int totalSum =0;while (n >0) {int d = n %10; n = n /10; totalSum += d * d; }return totalSum; }}