Finding Duplicate Values and Printing Them in an Array for C++

Question

I'm trying to find and print the duplicate values in from a list of 10 integers, and I already have this part for the C++ program figured to find it.

#include <iostream> 

using namespace std;

Program Main

int main() //Function Main

    int array[10], out[10];

cout << "The following numbers appear multiple times: ";

for (int i = 0; i < 10; i++)

    if (*(out + i) != 1)

        cout << *(out + i) << " ";

cout << "\n";

system("pause");

return 0;

Function to find duplicates

int* getDuplicateValues(int array[], int out[], int size)//Finds values that were used more than once in the program

for (int i = 0; i < 10; i++)

    out[i] = 1;

for (int i = 0; i < 10; i++)

{

    int count = 1;

    for (int j = i + 1; j < 10; j++)

    {

        if (array[i] == array[j])

            count++;
    }

    if (count > 1)

        out[i] = array[i];

    count++; 
}

return out;

The only problem is that it won't accept 1 as a duplicate value, and that is probably because of the coding on my part. And I'm relatively new to the coding process so all I need is a step in the right direction to forming the function correctly to find the duplicate values in the array. Please get back to me as soon as you can, preferably before Friday.

Sorry, should have been more specific, I'm also trying to have these values printed out — Daniel Bernal
– Daniel Bernal, Commented Dec 3, 2020 at 6:02

brc-dd · Accepted Answer · 2020-12-03 05:39:42Z

2

Currently two approaches are coming to my mind:

1 : Using sorting: Firstly just sort the array and then iterate over the elements to check if adjacent elements are same. If they are same then check if we have already copied them. If not then push them to a vector. And return the vector at last.

Implementation:

#include <algorithm>
#include <iostream>
#include <vector>

auto findDuplicates(std::vector<int> &&v) {
    std::sort(v.begin(), v.end());
    std::vector<int> res;
    for (size_t i = 1; i < v.size(); ++i)
        if (v[i] == v[i - 1] and (res.empty() or res.back() != v[i]))
            res.push_back(v[i]);
    return res;
}

int main() {
    auto v = findDuplicates({1, 2, 1, 1, 3, 3, 3, 4, 5, 4});
    for (auto &&i : v) std::cout << i << ' ';
}

2 : Using a map to store count: We can just map all elements of input vector to create something like a frequency table. And later iterate over it and check if count of an element is greater than 1.

Implementation:

#include <iostream>
#include <map>
#include <vector>

auto findDuplicates(std::vector<int> &&v) {
    std::map<int, size_t> cntMap;
    for (auto &&i : v) cntMap[i]++;
    std::vector<int> res;
    for (auto &&i : cntMap)
        if (i.second > 1) res.push_back(i.first);
    return res;
}

int main() {
    auto v = findDuplicates({1, 2, 1, 1, 3, 3, 3, 4, 5, 4});
    for (auto &&i : v) std::cout << i << ' ';
}

answered Dec 3, 2020 at 5:39

brc-dd

13.5k3 gold badges63 silver badges92 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Daniel Bernal Over a year ago

How about just using <iostream>?

brc-dd Over a year ago

@DanielBernal By just using iostream, the code will be much more longer and complicated if you implement the containers yourself. However, the first code (using sorting) can be easily done. Just make a sort function yourself and create arrays with new instead of using vector.

Collectives™ on Stack Overflow

Finding Duplicate Values and Printing Them in an Array for C++

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related