leetcode 202. Happy Number
题意
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
分析
- 同计算循环小数一样, 如果出现循环, 则无需继续计算,直接返回false即可.
- 否则循环计算每位数字的平方和，直到出现结果为1
代码
class Solution {
private:
long digitSquare(long num) {
long sum = 0;
while(num!=0) {
sum += pow(num%10, 2);
num /= 10;
}
return sum;
}
public:
bool isHappy(int n) {
unordered_map<int,bool> res;
if(n<=0)
return false;
n = digitSquare(n);
while(n != 1) {
if(res[n] == true)
return false;
res[n] = true;
n = digitSquare(n);
}
return true;
}
};
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