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How to find index of a given element in a Vector in C++
• Difficulty Level : Easy
• Last Updated : 29 Oct, 2020

Given a vector V consisting of N integers and an element K, the task is to find the index of element K in the vector V. If the element does not exist in vector then print -1.
Examples:

Input: V = {1, 45, 54, 71, 76, 17}, K = 54
Output:
Explanation :
The index of 54 is 2, hence output is 2.
Input: V = {3, 7, 9, 11, 13}, K = 12
Output: -1

Approach:
Follow the steps below to solve the problem:

• find(): Used to find the position of element in the vector.
• Subtract from the iterator returned from the find function, the base iterator of the vector .
• Finally return the index returned by the subtraction.

Below is the implementation of the above approach :

C++

 `// C++ program to find the index``// of an element in a vector``#include ``using` `namespace` `std;` `// Function to print the``// index of an element``void` `getIndex(vector<``int``> v, ``int` `K)``{``    ``auto` `it = find(v.begin(), v.end(), K);` `    ``// If element was found``    ``if` `(it != v.end())``    ``{``    ` `        ``// calculating the index``        ``// of K``        ``int` `index = it - v.begin();``        ``cout << index << endl;``    ``}``    ``else` `{``        ``// If the element is not``        ``// present in the vector``        ``cout << ``"-1"` `<< endl;``    ``}``}``// Driver Code``int` `main()``{``    ``// Vector``    ``vector<``int``> v = { 1, 45, 54, 71, 76, 17 };``    ``// Value whose index``    ``// needs to be found``    ``int` `K = 54;``    ``getIndex(v, K);``    ``return` `0;``}`
Output:
```2

```

Time Complexity: O(N)
Auxiliary Space: O(1)

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