Description
Write an algorithm to determine if a number n 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.
Return True if n is a happy number, and False if not.
Input: 19
Output: true
Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1
Analysis
判断环的两大方法
Hashset
class Solution {
public:
bool isHappy(int n) {
while(n!=1){
n=process(n);
if(a[n]==1)return 0;
a[n]=1;
}
return 1;
}
private:
int process(int x){
int sum=0;
while(x!=0){
int u=x%10;
sum+=u*u;
x/=10;
}
return sum;
}
int a[50000];
};
龟兔赛跑法
设定两个指针，一快一慢，快的一次走2步，慢的一次走1步
Code
class Solution {
public:
bool isHappy(int n) {
int a=n,b=n;
while(a!=1){
a=process(a);
a=process(a);
b=process(b);
if(a==b)break;
}
return a==1;
}
private:
int process(int x){
int sum=0;
while(x!=0){
int u=x%10;
sum+=u*u;
x/=10;
}
return sum;
}
};