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202.HappyNumber(easy).cpp
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202.HappyNumber(easy).cpp
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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
*/
class Solution {
public:
int get_digit_sum(int n)
{
int sum = 0;
vector<int> v;
while (n)
{
v.push_back(n%10);
n /= 10;
}
for (int i = 0;i<v.size();++i)
sum += v[i]*v[i];
return sum;
}
bool isHappy(int n) {
if (n == 1 )return true;
unordered_set<int> unset;
while(1)
{
int sum = get_digit_sum(n);
if (sum == 1) return true;
if (unset.count(sum) > 0) return false;
else
{
n = sum;
unset.insert(sum);
}
}
}
};