1. 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.

2. Runtime Distribution

3. Submission Details

4. Example

19 is a happy number
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

5. Code

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private HashSet set = new HashSet();

public boolean isHappy(int n) {
	if (n <= 0) {
		return false;
	}

	if (n == 1) {
		return true;
	}

	String num = String.valueOf(n);

	if (set.contains(num)) {
		return false;
	}

	set.add(num);

	int sum = 0;
	for (int i = 0; i < num.length(); i++) {
		int tmp = num.charAt(i) - '0';
		sum += tmp * tmp;
	}
	return isHappy(sum);
}

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6.Test

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import java.util.HashSet;

public class LeetCode0202 {

	private HashSet set = new HashSet();

	public boolean isHappy(int n) {
		if (n <= 0) {
			return false;
		}

		if (n == 1) {
			return true;
		}

		String num = String.valueOf(n);

		if (set.contains(num)) {
			return false;
		}

		set.add(num);

		int sum = 0;
		for (int i = 0; i < num.length(); i++) {
			int tmp = num.charAt(i) - '0';
			sum += tmp * tmp;
		}
		return isHappy(sum);
	}

	public static void main(String[] args) {
		LeetCode0202 leetcode = new LeetCode0202();
		System.out.println(leetcode.isHappy(19));
	}
}

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