1.描述
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
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1
2.分析
3.代碼
int squares(int n) {
int sum = 0;
while (n > 0) {
sum += (n % 10) * (n % 10);
n /= 10;
}
return sum;
}
bool isHappy(int n) {
if (n <= 0) return false;
int fast = n;
int slow = n;
for (;;) {
fast = squares(squares(fast));
slow = squares(slow);
if (1 == fast || 1 == slow) return true;
if (fast == slow) break;
}
return false;
}
