leetcode 30day--2
202. Happy Number
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.
Example:
Input: 19
Output: true
Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1
class Solution {
public:
//主要是判断平方和是否会重复,如果重复就会造成cycle,否则就可以一直算下去,直到为1
long help(int n){
long res = 0;
while(n){
res += (n%10)*(n%10);
n=n/10;
}
return res;
}
bool isHappy(int n) {
if(n == 1){
return true;
}
if(m.find(n) != m.end()) return false;
else{
m[n] = true;
return isHappy(help(n));
}
}
private:
map<int,bool> m;
};
很巧妙,借鉴链表的快慢指针
class Solution {
public:
//借鉴链表是否有环的快慢指针法
long help(long n){
long res=0;
while(n){
long tmp = n%10;
n = n/10;
res += tmp*tmp;
}
return res;
}
bool isHappy(int n) {
long slow=n,fast=n;
do{
slow = help(slow);
fast = help(fast);
fast = help(fast);
if(slow == 1 || fast == 1) return true;
}while(slow != fast); return false;
}
};
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