Nth Fibonacci number
Return the nth number in the Fibonacci sequence, counting from zero.
- fib(0) is 0 and fib(1) is 1; every later term is the sum of the two before it.
- n stays within 0..45.
fibonacci(n: int) → int
C++ needs a compiler and Drill does not host one yet, so this page is the reference rather than an exercise: the problem, worked examples, and the solution in full. To type it out, the same problem runs in Python.
Where you start
int fibonacci(int n) {
}Worked examples
| Call | Result |
|---|---|
fibonacci(0) | 0 |
fibonacci(1) | 1 |
fibonacci(2) | 1 |
fibonacci(10) | 55 |
Hint
Keep two variables and slide them forward. No recursion needed.
Reference solution in C++
int fibonacci(int n) {
int a = 0, b = 1;
for (int i = 0; i < n; i++) {
int next = a + b;
a = b;
b = next;
}
return a;
}