LeetCode Link: https://leetcode.com/problems/fibonacci-number/
Language: C#
Problem Statement
The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,
F(0) = 0, F(1) = 1
F(n) = F(n - 1) + F(n - 2), for n > 1.
Given n, calculate F(n).
Examples
Example 1:
Input: n = 2
Output: 1
Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.
Example 2:
Input: n = 3
Output: 2
Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.
Example 3:
Input: n = 4
Output: 3
Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.
Constraints
- 0 <= n <= 30
Solution
public class Solution
{
private Dictionary<int, int> fibs = new Dictionary<int, int>
{
{0,0},
{1,1}
};
public int Fib(int n)
{
if (fibs.ContainsKey(n))
{
return fibs[n];
}
var f = Fib(n-1) + Fib (n-2);
fibs[n] = f;
return f;
}
}
Complexity
Time Complexity: O(N)
Space Complexity: O(N)
Notes
I have used Memoization/Dynamic Programming method in this solution. It is also possible to perform the same with plain old for/while loop or recursion.