LeetCode 202. 快乐数 Happy Number

Posted 2020-12-23 zsy-blog

 

 解法一：哈希表

class Solution {
public:
    bool isHappy(int n) {
        set<int> seen;
        while (n != 1 && !seen.count(n))  //快乐或者存在环跳出
        {
            seen.insert(n);
            n = getNext(n);
        }
        return n == 1;
    }

    int getNext(int n)
    {
        int totalSum = 0;
        while (n > 0)
        {
            int d = n % 10;
            totalSum += d * d;
            n = n / 10;
        }
        return totalSum;
    }
};

 

解法二：快慢指针

class Solution {
public:
    bool isHappy(int n) {
        int slow = n;
        int fast = getNext(n);
        while (slow != 1 && slow != fast)  //快乐或者存在环跳出
        {
            slow = getNext(slow);
            fast = getNext(getNext(fast));
        }
        return slow == 1;
    }

    int getNext(int n)
    {
        int totalSum = 0;
        while (n > 0)
        {
            int d = n % 10;
            totalSum += d * d;
            n = n / 10;
        }
        return totalSum;
    }
};