202 LeetCode Java: Happy Number – Easy¶
Problem:¶
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
Thoughts:¶
This is a very straight forward integer problem. Just do the formula addition, and then check if the result is one.
Do this repeatedly until 1 occurs or same appearing number appears twice. Using a HashSet to keep appearing number is helpful.
Solutions:¶
public class Solution {
private HashSet<Integer> visited = new HashSet<Integer>();
public boolean isHappy(int n) {
while(true){
if (visited.contains(n)){
return false;
}
else{
int val = sum(n);
if (val == 1){
return true;
}
else{
visited.add(n);
n = val;
}
}//else
}//while true
}
private int sum(int n){
int result = 0;
while (n != 0){
result += Math.pow(n % 10, 2);
n = n / 10;
}
return result;
}
}
public class Solution {
public boolean isHappy(int n) {
HashSet<Integer> data = new HashSet<Integer>();
while (true) {
int r = process(n);
if (r == 1) {
return true;
}
if (data.contains(r)) {
return false;
}
data.add(r);
n = r;
}
}
private int process(int n) {
int result = 0;
while (n != 0) {
result += (n % 10) * (n % 10);
n = n / 10;
}
return result;
}
}