Happy Number
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
Solution
按照规律算即可,如果出现循环就证明不可能
Complexity
时间复杂度 O(n2 ),空间复杂度 O(n)
Code
public class Solution {
int trans(int n){
int s = 0;
do{
int t = n % 10;
s += t * t;
n /= 10;
} while(n > 0);
return s;
}
public boolean isHappy(int n) {
Set<Integer> s = new HashSet<>();
for(;;) {
n = trans(n);
if(n == 1) return true;
if(s.contains(n)) return false;
s.add(n);
}
}
}