202. Happy Number
Easy
Write an algorithm to determine if a number n
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.
Return True if n
is a happy number, and False if not.
Example:
Input: 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1
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//C++: 10ms class Solution { public: bool isHappy(int n) { unordered_set<int> cycle; while(n>1 && cycle.find(n)==cycle.end()){ cycle.insert(n); int sum = 0; while(n){ int t = n%10; sum += t*t; n = (n-t)/10; } n = sum; } return n==1; } }; //Java class Solution { int getNext (int n) { int ret = 0; while(n>0) { int d = n%10; ret += d*d; n = n/10; } return ret; } public boolean isHappy(int n) { Set<Integer> set = new HashSet<>(); while(n!=1 && !set.contains(n)) { set.add(n); n = getNext(n); } return n == 1; } }
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