> For the complete documentation index, see [llms.txt](https://gl01.gitbook.io/gfg-editorials/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://gl01.gitbook.io/gfg-editorials/2024/03-2024-march-19/23-fibonacci-series-up-to-nth-term.md).

# 23. Fibonacci series up to Nth term

The problem can be found at the following link: [Question Link](https://www.geeksforgeeks.org/problems/fibonacci-series-up-to-nth-term/1)

## My Approach

* Initialize an empty vector vec to store the Fibonacci series.
* Initialize variables n1 and n2 with initial Fibonacci values.
* If n is 0, push n1 into vec and return vec.
* If n is 1, push both n1 and n2 into vec and return vec.
* For i starting from 2 up to n, calculate the next Fibonacci number by adding the last two elements of vec, take modulo mod, and push it into vec.
* Return the vec vector containing the Fibonacci series.

## Time and Auxiliary Space Complexity

* **Time Complexity**: The time complexity of this approach is `O(N)`, because it iterates N times to generate the Fibonacci series.
* **Auxiliary Space Complexity**: The auxiliary space complexity is `O(N)`, where N is the user input.

## Code (C++)

```cpp
class Solution {
  public:
    const int mod=1e9+7;
    vector<int> Series(int n)
    {
        vector<int>vec;
        int n1=0, n2=1;
        vec.push_back(n1);
        if (n==0)
            return vec;
        vec.push_back(n2);
        if (n==1)
            return vec;
        for (int i=2;i<=n;i++)
        {
            int num=(vec[i-1]+vec[i-2])%mod;
            vec.push_back(num);
        }
        return vec;
    }
};
```

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