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HappyNumber.java

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/*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*/

public class Solution {

private int getNextHappy(int n) {

int sum = 0;

while (n != 0) {

sum += (n % 10) * (n % 10);

n /= 10;

}

return sum;

}

public boolean isHappy(int n) {

HashSet<Integer> hash = new HashSet<Integer>();

while (n != 1) {

if (hash.contains(n)) {

return false;

}

hash.add(n);

n = getNextHappy(n);

}

return true;

}

}

// Discussion

public class Solution {

public boolean isHappy(int n) {

int x = n;

int y = n;

while(x>1){

x = cal(x) ;

if(x==1) return true ;

y = cal(cal(y));

if(y==1) return true ;

if(x==y) return false;

}

return true ;

}

public int cal(int n){

int x = n;

int s = 0;

while(x>0){

s = s+(x%10)*(x%10);

x = x/10;

}

return s ;

}

}