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
一刷
題解：如果不停地拆分并求digit square sum， 可能陷入一種循環(huán)。如果最終收斂在1伦吠，那么表示是happy的毒涧，如果是不停地重復(fù)幾個數(shù)字，那么是unhappy的徙邻。這是終止條件购裙。于是這個可以借鑒linkedlist是否有環(huán)的快慢指針來做。
public class Solution {
private int digitSquareSum(int n){
int sum = 0, tmp;
while(n>0){
tmp = n%10;
sum += tmp*tmp;
n /= 10;
}
return sum;
}
public boolean isHappy(int n) {
int slow, fast;
slow = fast = n;
do{
slow = digitSquareSum(slow);
fast = digitSquareSum(fast);
fast = digitSquareSum(fast);
}while(slow!=fast);
if(slow == 1) return true;
else return false;
}
}
