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Solution.java
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Solution.java
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package happynumber;
import java.util.ArrayList;
import java.util.List;
/**
* 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
*
*/
class Solution {
public boolean isHappy(int n) {
List<Integer> sums = new ArrayList<>();
while(true) {
if (n == 1)
return true;
else {
int tsum = 0;
while(n > 0) {
int curr_digit = n % 10;
int curr_square = curr_digit * curr_digit;
tsum += curr_square;
n /= 10;
}
if(sums.contains(tsum)) {
return false;
}
sums.add(tsum);
n = tsum;
}
}
}
}
/*
Runtime: 1 ms, faster than 97.86% of Java online submissions for Happy Number.
Memory Usage: 36.4 MB, less than 6.06% of Java online submissions for Happy Number.
*/