How can I find minimum and unique element of array in c++? - c++

Question

I have array(of numbers) with size N. I need to find minimum element which is unique,so if arr[5] ={1,2,3,1,2}, answer is 3.
I tried that with following code:
Int n = sizeof(arr)/sizeof(arr[0]);
sort(arr,arr + n);
for(int i = 0;i<N;i++){
for(int j = 0;j<N;j++){
if(arr[i] == arr[j]){
remove(arr,arr+n,i);
remove(arr,arr+n,j);
}
}
}
But problem is that this only work if I have 2 identical elements of arr.I could create if conditions for number of identical, but I can have 3 or 4 or 1000,so it will be pretty odd. So what is more elagant way to do this? Thank you in advance.

Answer 1

try this code, this uses an unordered map
int m = 2147483647;
int int_array[] = { 1,2,3,3,1,6,7,7,9 };
unordered_map<int, int> map;
for (int i = 0; i < sizeof(int_array) / sizeof(int_array[0]); i++) {
map[int_array[i]] = map[int_array[i]] + 1;
}
unordered_map<int, int>::iterator itr;
for (itr = map.begin(); itr != map.end(); itr++)
{
if (itr->second == 1) {
if (itr->first < m) {
m = itr->first;
}
}
}
printf("minimum unique is %d", m);

Answer 2

after sorting the array you can count the number of the dublicated members , if the member is unique then its count equals zero :
int main()
{
int arr[] = { 1, 2, 1, 3, 4, 1, 2 };
int n = sizeof(arr) / sizeof(int);
sort(arr, arr + n);
int count = 0;
int unique = -1;
for (int i = 0; unique == -1 && i < n - 1; ++i) {
if (arr[i] != arr[i + 1]) {
if (count==0)
unique = arr[i];
else
count = 0;
}
else {
count++;
}
}
if (count == 0 && unique ==-1)
unique = arr[n-1];
cout << unique;
return 0;
}

Answer 3

I propose the following code:
#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
int arr[5] = { 1,2,3,2,1 };
int N = sizeof(arr) / sizeof(arr[0]);
sort(arr, arr + N);
int index = -1;
// Check first element is different comparing with second one.
// If the array is only one element, then first element is unique
if (N == 1 || arr[0] != arr[1]) {
index = 0;
}
else {
int i = 1;
while (i < N - 1 && index == -1) {
// Check number is different to previous and different to next value
if (arr[i - 1] != arr[i] && arr[i] != arr[i + 1]) {
index = i;
}
else
{
i++;
}
}
if (index == -1) {
// No found, check last element comparing with previous
if (arr[i - 1] != arr[i]) {
index = i;
}
}
}
if (index != -1) {
// Have found min value
cout << "Min not repeated value is " << arr[index] << endl;
}
else {
// All elements are repeated
cout << "No min value" << endl;
}
}
Once the array is sorted, I compare each value with previous and next value to check it is unique. But for first and last element are a special case.

Answer 4

Using what I said in the comments, with an extra bool.
int arr[] = { 1, 2, 1, 3, 4, 1, 2 };
int n = sizeof( arr ) / sizeof( int );
std::sort( arr, arr + n );
bool match = false;
for ( int i = 0; i < n; ++i ) {
if ( i == n - 1 || arr[i] != arr[i + 1] ) {
if ( match )
match = false;
else
return arr[i];
} else {
match = true;
}
}
return -1; // made up number in case all duplicates
If the two values are equal, then we know that we can't use that value again, so I set match to true. If they are not equal, then if it was already disqualified, I ignore it and set match back to false, otherwise, return that value.
There are more elegant ways to do this; this is just the simplest.