202. Happy Number

Leetcode Hash Table Math

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

分析

直接采用题目所定义的Happy Number来写。采用HashSet判断重复。

public boolean isHappy(int n) {
    HashSet set = new HashSet();
    while (n != 1) {
        if (!set.add(n)) return false;
        int nt = n, digit;
        n = 0;
        while (nt != 0) {
            digit = nt % 10;
            n += digit*digit;
            nt /= 10;
        }
    }
    return true;
}