Happy Number
Description
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
Solution
首先定义一个函数计算每个digit平方和,新建一个set,如果以前出现过该数字,则表明不是happy number,如结果为1, 则表示是happy number。
class Solution {
public boolean isHappy(int n) {
Set<Integer> set = new HashSet<Integer>();
while (n > 1 && !set.contains(n)) {
set.add(n);
n = calculate(n);
}
return n == 1;
}
private int calculate(int n) {
int sum = 0;
int d = 0;
while (n != 0) {
d = n % 10;
sum += d*d;
n = n / 10;
}
return sum;
}
}