print duplicate elements in array - c++

Question

I want to find duplicate elements in a dynamic array. In most cases it works, but how can it work for this case. I'm finding duplicate elements in a given array. But there is one problem that my duplicate elements can repeat too. How can I solve that part.
#include <iostream>
int main() {
unsigned n;
std::cin >> n;
int count = 0;
int* dynArr = new int[n];
for (int i = 0; i < n; i++) {
std::cin >> dynArr[i];
}
for(int i = 0; i < n; i++){
for(int j = i + 1; j < n; j++){
if(dynArr[j] == dynArr[i]){
std::cout<<dynArr[j]<<" ";
break;
}
}
}
}
I have a problem with this part. When I'm inputting a my array length 6, and elements {1,1,2,1,2,2}.
I got (1,1,2,2).
But I need to get only 1,2.
input 6
1 1 2 1 2 2
output 1 1 2 2
but must be
output 1 2

Answer 1

Here's a simple and fast solution.
std::map<int,size_t> element_count;
for(int i = 0; i < n; i++){
if ( ++element_count[dynArr[i]] == 2 ){
// Only report on the second occurrance
std::cout<<dynArr[j]<<" ";
}
}

Answer 2

const int listSize = 5;
int list1[listSize] = {0,0,1,1,3};
bool dupList[listSize] = {false};
for (int index = 0; index < listSize; index++) {
int val = list1[index];
for (int i = 0; i < listSize; i++) {
if (i != index) {
if (list1[i] == val) {
dupList[index] = true;
}
}
}
}
int printList[listSize];
int addNum = 0;
for (int index = 0; index < listSize; index++) {
if (dupList[index] == true) {
bool run = true;
int print = list1[index];
for (int i = 0; i < listSize; i++) {
if (printList[i] == print) {
run = false;
}
}
if (run == true) {
std::cout << print << " ";
printList[addNum] = print;
addNum++;
}
}
}
Note this code will NOT run quickly at all only use it if the operation does not need to get run very many times but it will only display the single numbers that are duplicates. It will defernatly need to get optimised more

Answer 3

You can simply get it done using two std::set<int>s.
#include <set>
#include <iostream>
int main() {
unsigned n;
std::cin >> n;
int count = 0;
std::set<int> all;
std::set<int> redundant;
for (int i = 0; i < n; i++) {
int input = 0;
std::cin >> input;
// You cant enter the entry because its present. This will return a std::pair<,> with the second value false.
if (!all.insert(input).second)
redundant.insert(input); // We store this in another set so we dont duplicate the redundant entries.
}
for (auto itr = redundant.begin(); itr != redundant.end(); itr++)
std::cout << *itr << " ";
}