LeetCode: Happy Number

Key is how to test the number loops endlessly. Test loop by a hashmap recording all sums appeared. If same sum appear again, it's easy to see the sum of the squares of its digits will loop.

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class Solution { public: int getSum(int n){ int sum=0; while(n){ sum+=(n%10)*(n%10); n=n/10; } return sum; } bool isHappy(int n) { unordered_set<int> record; while(n!=1){ if(record.count(n)) return false; else record.insert(n); n=getSum(n); } return true; } };