1. 题目
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
- 1 2 + 9 2 = 82
- 8 2 + 2 2 = 68
- 6 2 + 8 2 = 100
- 1 2 + 0 2 + 0 2 = 1
简单的水题，用hash表去判断有无重复。一个巧妙的解题思路是，对于循环重复的情况，可以用slow和fast两个变量来代替hash表。
class Solution {
public:
bool isHappy(int n) {
if (n < 1)
return false;
if (n == 1)
return true;
unordered_set<int> showedNums;
showedNums.insert(n);
while(true) {
int s = 0;
while(n){
s +=(n%10)*(n%10);
n = n / 10;
}
if(s==1)
return true;
else if(showedNums.find(s)!=showedNums.end())
return false;
n = s;
showedNums.insert(s);
}
}
};
class Solution {
public:
int cal(int n){
int s = 0;
while(n){
s +=(n%10)*(n%10);
n /= 10;
}
return s;
}
bool isHappy(int n) {
if (n < 1)
return false;
if (n == 1)
return true;
int slow=n,fast=n;
do {
slow = cal(slow);
fast = cal(fast);
fast = cal(fast);
}while(slow != fast);
if(slow ==1) return 1;
else return 0;
}
};版权声明：本文为博主原创文章，未经博主允许不得转载。