How to Replace Second Occurrence of an Element from a Vector?

In C++, a vector is a dynamic array that can grow and shrink in size as needed. In this article, we will learn how to replace the second occurrence of a specific element in a vector.

Example:

Input:
myVector = { 5,2,8,5,8,8}
Element: 8
Replacement: 10

Output:
myVector = { 5,2,8,5,10,8}

Replace Second Occurrence of an Element in a Vector

To replace the second occurrence of a specific element in a std::vector in C++, we can use the std::find() function to find the first occurrence of the element, and then use std::find() again to find the second occurrence. Once we have found the second occurrence, we can replace it directly in the vector using the std::vector::erase() function.

C++ Program to Replace the Second Occurrence of an Element in a Vector

The below example demonstrates the use of std::find() function to replace the second occurrence of a specific element in a vector in C++.

C++

// C++ Program to illustrate how to replace the second
// occurrence of a specific element in a vector.
#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

void replaceSecondOccurrence(vector<int>& vec, int element,
                             int replacement)
{
    // Find the first occurrence
    auto it = find(vec.begin(), vec.end(), element);

    // If the element is found, find the second occurrence
    if (it != vec.end()) {
        it = find(it + 1, vec.end(), element);

        // If the second occurrence is found, replace it
        if (it != vec.end()) {
            *it = replacement;
        }
    }
}

int main()
{
    // Vector declaration
    vector<int> vec = { 5, 2, 8, 5, 8, 8 };

    // Element to replace and its replacement
    int element = 8;
    int replacement = 10;

    // Replacing the second occurrence of specific element
    replaceSecondOccurrence(vec, element, replacement);

    // Printing the vector after replacement
    cout << "Vector after replacing second occurrence of "
         << element << ": ";
    for (int i : vec) {
        cout << i << " ";
    }
    cout << endl;

    return 0;
}

Output

Vector after replacing second occurrence of 8: 5 2 8 5 10 8 

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