# dennyzhang/code.dennyzhang.com

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# Leetcode: Fibonacci Number

Fibonacci Number

Similar Problems:

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).

Example 1:

```Input: 2
Output: 1
Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.
```

Example 2:

```Input: 3
Output: 2
Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.
```

Example 3:

```Input: 4
Output: 3
Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.
```

Note:

• 0 <= N <= 30.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

```// Blog link: https://code.dennyzhang.com/fibonacci-number
// Basic Ideas:
// Complexity: Time O(n), Space O(1)
func fib(N int) int {
if N <= 0 { return N }
p, q, i := 0, 1, 1
for i < N {
q, p = q+p, q
i++
}
return q
}```