题目要求：
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
Credits:
Special thanks to @mithmatt and @ts for adding this problem and creating all test cases.
这道题比较需要注意的一点是要在合适的时候跳出死循环。程序如下：
class Solution {
public:
bool isHappy(int n) {
vector<int> vec;
vec.push_back(n);
while(n!= )
{
int sum = ;
int tmpN = n;
while(tmpN != )
{
sum += (tmpN % ) * (tmpN % );
tmpN /= ;
}
n = sum;
if(find(vec.begin(), vec.end(), n) != vec.end())
break;
else
vec.push_back(n);
}
return n == ;
}
};
改为用哈希表来实现的程序如下：
class Solution {
public:
bool isHappy(int n) {
unordered_map<int, int> hashMap;
hashMap[n] = n;
while(n != )
{
int sum = ;
int tmpN = n;
while(tmpN != )
{
sum += (tmpN % ) * (tmpN % );
tmpN /= ;
}
n = sum;
if(hashMap.find(n) != hashMap.end())
break;
else
hashMap[n] = n;
}
return n == ;
}
};