Problem
Start with n. If it is even, divide it by 2; if it is odd, multiply it by 3 and add 1. Repeat until the value is 1. Include both the starting value and the final 1 in your answer.
Implement collatz_sequence(n).
Input
n: The positive starting integer.
Output
Return the complete sequence in order.
Constraints
1 ≤ n ≤ 10,000. Inputs in this range reach 1 under this rule; all sequence values fit a signed 64-bit integer.
Examples
Input:
n = 6
Expected output:
expected = [6, 3, 10, 5, 16, 8, 4, 2, 1]Input:
long long n = 6;
Expected output:
std::vector<long long> expected = {6, 3, 10, 5, 16, 8, 4, 2, 1};Input:
long n = 6;
Expected output:
long[] expected = new long[] {6, 3, 10, 5, 16, 8, 4, 2, 1};Explanation
6 is even, so it becomes 3. Then 3 becomes 10. Continue applying the rule until 1.
Input:
n = 1
Expected output:
expected = [1]Input:
long long n = 1;
Expected output:
std::vector<long long> expected = {1};Input:
long n = 1;
Expected output:
long[] expected = new long[] {1};Explanation
The starting value is already 1, so no transformations are needed.
How to approach it
Try on your own first, then open one hint at a time.
Hint 1
The sequence is generated by repeatedly applying one rule based on whether the current number is even or odd.
Hint 2
Keep appending each new value until you reach 1.
Hint 3
Watch out that the starting value itself and the final 1 must both appear in the result.
Expected complexity
O(k) time, O(k) extra space, where k is the sequence length
References
This challenge is adapted for CodeUtility. Follow the statement and constraints above.