202. Happy Number

作者 汪小祯 日期 2017-02-05
202. Happy Number

题目

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

题解 Byself

额外写了两个函数
一个用来计算每位数字的平方和
一个用来判断是否=1

class Solution {
public:
int a=0;
int temp=0;
int all=0;
int num(int n){
if (n<10) {
return all+pow(n, 2);
}
else{
all+=pow((n%10),2);
return num(n/10);
}
}
void isHapp(int n){
if (n==1) {
a=1;
}
else {
all=0;
isHapp(num(n));
}
}
bool isHappy(int n) {
isHapp(n);
if (a==1) {
return true;
}
else
return false;
}
};

后来看了别人的解法,果然三个可以放在一个里面。。。

优解

class Solution {
public:
bool isHappy(int n) {
while (true) {
int sum=0;
if (n==1) return true;
if(n==4) return false;
while (n) {
sum+=(n%10)*(n%10);
n/=10;
}
n=sum;
}
}
};