Happy number--Leetcode

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 and replace the number by the Sum of the squares of its digits, and repeat the process until the number equals 1 (where it would stay), or it loops Endl essly in a cycle which does not include 1. Those numbers for which this process ends in 1 is happy numbers.

Example: is a happy number

• 12 + 92 = 82
• 82 + 22 = 68
• 62 + 82 = 100
• 12 + 02 + 02 = 1

Algorithm One,

Since there is the possibility of a dead loop, use a collection to record the numbers that have been accessed. If it appears in the collection, a loop occurs.

Spents 8ms on Leetcode.

Class Solution {public:    bool Ishappy (int n) {        unordered_set<int> visited;        while (n! = 1 &&!visited.count (n)) {            visited.insert (n);            int number = 0;            while (n) {number                + = (n%) * (n%);                n/=;            }            n = number;        }        return  n = = 1;    }};

Algorithm two, fast and slow pointer

The use of collections in the end will occupy extra space.

The concept of fast and slow pointers is used here to detect the existence of a dead loop.

The actual execution time on the Leetcode is 4ms.

Class Solution {public:    bool Ishappy (int n) {        int slow = n, fast = n;        Do {            slow = next (slow);            Fast = Next (next (fast));        } while (slow! = fast);        return slow = = 1;    }        int next (int n) {        int ans = 0;        while (n) {            ans + = (n) * (n) n/=;        }        return ans;    };

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

Happy number--Leetcode