How to find index of a given element in a Vector in C++

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 = 54Output:2Explanation :

The index of 54 is 2, hence output is 2.Input:V = {3, 7, 9, 11, 13}, K = 12Output:-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 <bits/stdc++.h>` `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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