1.9 KiB
1.9 KiB
Leetcode Happy-Number
2022-07-26 09:12
Algorithms:
#algorithm #Floyd_s_cycle_finding_algorithm
Difficulty:
#coding_problem #difficulty-easy
Additional tags:
#leetcode
Revisions:
N/A
Related topics:
Links:
Problem
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.
- 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.
Return true if n is a happy number, and false if not.
Examples
Example 1:
Input: n = 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1
Example 2:
Input: n = 2 Output: false
Constraints
1 <= n <= 231 - 1
Thoughts
[!summary] This is a #Floyd_s_cycle_finding_algorithm
This works, because as the problem mentioned, this will result in a endless loop.
So, by using fast ans slow, we can determine whether there is a loop.
And, when fast hit 1, we know slow will eventually reach the answer, so we return early. (but in the cost of time of checking).
Solution
class Solution {
int getDigitSqrt(int i) {
int sum = 0;
while (i) {
sum += (i % 10) * (i % 10);
i /= 10;
}
return sum;
}
public:
bool isHappy(int n) {
// Floyd cycle finding algorighm.
int slow, fast;
slow = fast = n;
do {
slow = getDigitSqrt(slow);
fast = getDigitSqrt(fast);
fast = getDigitSqrt(fast);
if (fast == 1) {
return true;
}
} while (fast != slow);
return false;
}
};