unordered_set emplace_hint() function in C++ STL

The unordered_set::emplace_hint() function is an inbuilt function in C++ STL which inserts a new element in the unordered_set only if the value to be inserted is unique, with a given hint. 

Syntax:

unordered_set_name.emplace_hint( position, value )

Parameter: This function accepts two parameters as mentioned above and described below:

• position: This parameter is used to describe the position for inserted operation.
• value: This parameter is used to hold the which needs to insert.

Return Value: If the value is not present in the unordered_set, then the function inserts the value and returns an iterator pointing to the inserted element. Else, if the value is already present in the unordered_set, then the function returns the iterator pointing to that element. 

Below program illustrates the unordered_set::emplace_hint() function in C++ STL: 

Program 1:

CPP

// CPP program to illustrate
// unordered_set::emplace_hint() function
#include <iostream>
#include <unordered_set>
using namespace std;

// main program
int main()
{

    // Initialize an unordered_set
    unordered_set<int> uset = { 20, 40, 50, 60 };

    // Insert an element that is not present
    uset.emplace_hint(uset.begin(), 80);

    // Display uset
    cout << "uset: ";
    for (auto it = uset.begin(); it != uset.end(); it++)
        cout << *it << " ";
}

Output:

uset: 80 20 40 50 60

Program 2:

CPP

// CPP program to illustrate
// unordered_set::emplace_hint() function
#include <iostream>
#include <unordered_set>
using namespace std;

// main program
int main()
{

    // Initialize an unordered_set
    unordered_set<int> uset = { 20, 40, 50, 60 };

    // Try to Insert an element that is not present
    uset.emplace_hint(uset.begin(), 50);

    // Display uset
    cout << "uset: ";
    for (auto it = uset.begin(); it != uset.end(); it++)
        cout << *it << " ";
}

Output:

uset: 60 50 40 20

Time complexity: O(n)