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
- 12 92 = 82
- 82 22 = 68
- 62 82 = 100
- 12 02 02 = 1
- 使用set 对每一个计算的结果进行计算，如果是1则是Happy Number；不是1且在set中出现过，则不是返回false；否则将结果加入set。
- 利用性质，特殊数字“4” 在某一时刻，出现了4的Number肯定不Happy。
public boolean isHappy(int n) {
if (n < 1) {
return false;
}
if (n == 1) {
return true;
}
Set<Integer> set = new HashSet<Integer>();
set.add(n);
while (true) {
int s = 0;
while (n > 0) {
s = (n % 10) * (n % 10);
n /= 10;
}
System.out.println(s);
if (s == 1) {
return true;
} else if (set.contains(s)) {
return false;
}
set.add(s);
n = s;
}
} public boolean isHappy2(int n) {
if (n < 1) {
return false;
}
if (n == 1) {
return true;
} else if (n == 4) {
return false;
}
int s = 0;
while (n > 0) {
s = (n % 10) * (n % 10);
n /= 10;
}
return isHappy2(s);
}
