leetcode 202: Happy Number

Happy Number

Total Accepted: 3585 Total Submissions: 10859

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

[思路]

同计算循环小数一样, 如果出现循环, 则无需继续计算,直接返回false即可.

[code]

public class Solution {
    public boolean isHappy(int n) {
        if(n<=0) return false;
        long ln = n;
        Set<Long> set = new HashSet<Long>();
        
        while(ln<=Integer.MAX_VALUE) {
            if((ln) ) return false; else (ln);
            ln = digitSquare(ln);
            if(ln == 1) return true;
        }
        return false;
    }
    
    private long digitSquare(long ln) {
        long sum = 0;
        while(ln!=0) {
            sum += (ln%10, 2);
            ln /= 10;
        }
        return sum;
    }
}