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# Fibonacci Number

## [Fibonacci Number](https://leetcode.com/problems/fibonacci-number)

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: 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`

## Solutions

### 🧠 Cpp

```cpp
class Solution
{
    //max n == 30
     array<int, 31> _storage = {0,1};
public:
    constexpr int fib(int n)
    {
        if(n && !_storage[n])
            _storage[n] = fib(n-1) + fib(n-2);

        return _storage[n];
    }
};
```