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
朴素的解法。用快慢指针来标记环路。
#include <iostream>
#include <vector>
using namespace std;
class Solution {
public:
bool isHappy(int n) {
int slow = solve_num(n);
int fast = solve_num(slow);
if (slow == 1)
return true;
while (slow != fast) {
slow = solve_num(slow);
if (slow == 1)
return true;
fast = solve_num(fast);
fast = solve_num(fast);
}
return false;
}
int solve_num(int n) {
int bw = 0;
int sum = 0;
while (n != 0) {
bw = n % 10;
sum += bw * bw;
n /= 10;
}
return sum;
}
};
