Problem:
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:
Input: 19
Output: true
Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1
思路：
Solution (C++):
bool isHappy(int n) {
vector<int> res = digit(n);
int ans = square_sum(res);
if (ans == 1) return true;
set<int> s;
s.insert(ans);
while (ans != 1) {
res = digit(ans);
ans = square_sum(res);
if (ans == 1) return true;
if (s.find(ans) != s.end()) return false;
else s.insert(ans);
}
return false;
}
vector<int> digit(int n) {
vector<int> dig;
if (n == 0) { dig.push_back(0); return dig; }
while (n) {
dig.push_back(n%10);
n /= 10;
}
return dig;
}
int square_sum(vector<int> &v) {
int sum = 0;
for (auto num: v) sum += num * num;
return sum;
}
性能：
Runtime: 8 ms Memory Usage: 6.8 MB
思路：
Solution (C++):
性能：
Runtime: ms Memory Usage: MB
