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:
Input: 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1
本题要判断一个数是否是Happy Number,过程是:不断对数的每个digit求平方和,如果平方和等于1,则是Happy Number;如果造成无限循环了,则不是Happy Number。 代码很简单,直接按题意做就是,使用set判断是否出现重复循环了。完整代码如下:
class Solution {
public:
bool isHappy(int n)
{
set<int> nums;
while (true) {
if (nums.find(n) != nums.end())
return false;
nums.insert(n);
int sum = 0;
while (n != 0) {
int q = n % 10;
sum += q * q;
n = n / 10;
}
if (sum == 1)
return true;
else
n = sum;
}
}
};
本代码提交AC,用时4MS。