LonelyInteger.cpp

#include <vector>
#include <string>
#include <functional>
#include <iostream>
#include <algorithm>

using namespace std;

string ltrim(const string &);
string rtrim(const string &);
vector<string> split(const string &);

/*
 *
 * The function is expected to return an INTEGER.
 * The function accepts INTEGER_ARRAY a as parameter.
 */

int lonelyinteger(vector<int> a) {
    while(!a.empty()) {
        bool found = false;
        int currentElement = a.back();
        a.pop_back();
        if(a.empty()) return currentElement;
        for(int i = 0; i < a.size(); i++) {
            if(a[i] == currentElement) {
                a.erase(a.begin() + i);
                found = true;
                break;
            }
        }
        if(!found) return currentElement;
    }
    return -1;
}

int main()
{
    string n_temp;
    getline(cin, n_temp);

    int n = stoi(ltrim(rtrim(n_temp)));
    
    string a_temp_temp;
    getline(cin, a_temp_temp);
    vector<string> a_temp = split(rtrim(a_temp_temp));
    
    vector<int> a(n);

    for (int i = 0; i < n; i++) {
        int a_item = stoi(a_temp[i]);

        a[i] = a_item;
    }
    int result = lonelyinteger(a);

    cout << "Result: " << result << "\n";

    return 0;
}

string ltrim(const string &str) {
    string s(str);

    s.erase(
        s.begin(),
        find_if(s.begin(), s.end(), [](int c) {return !std::isspace(c);})
    );

    return s;
}

string rtrim(const string &str) {
    string s(str);

    s.erase(
        find_if(s.rbegin(), s.rend(), [](int c) {return !std::isspace(c);}).base(),
        s.end()
    );

    return s;
}

vector<string> split(const string &str) {
    vector<string> tokens;

    string::size_type start = 0;
    string::size_type end = 0;
    while ((end = str.find(" ", start)) != string::npos) {
        tokens.push_back(str.substr(start, end - start));
        start = end + 1;
    }
    tokens.push_back(str.substr(start));

    return tokens;
}