pairs.cpp

#include <bits/stdc++.h>

using namespace std;

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

/*
 * Complete the 'pairs' function below.
 *
 * The function is expected to return an INTEGER.
 * The function accepts following parameters:
 *  1. INTEGER k
 *  2. INTEGER_ARRAY arr
 */

int pairs(int k, vector<int> arr)
{
    int match = 0;
    int diff = k;
    unordered_set<int> set;
    for (int i : arr)
    {
        set.insert(i);
    }
    for (int i = 0; i < arr.size(); i++)
    {
        // check if pair with the given difference `(arr[i], arr[i]-diff)` exists
        if ((set.find(arr[i] - diff) != set.end()))
        {
            // cout << "(" << arr[i] << ", " << arr[i] - diff << ")\n";
            match++;
        }

        // check if pair with the given difference `(arr[i]+diff, arr[i])` exists
        if ((set.find(arr[i] + diff) != set.end()))
        {
            // cout << "(" << arr[i] + diff << ", " << arr[i] << ")\n";
            match++;
        }

        // insert the current element into the set
        // set.insert(arr[i]);
        set.erase(set.find(arr[i]));
    }
    cout << match;
    return match;
}

int main()
{
    ofstream fout(getenv("OUTPUT_PATH"));

    string first_multiple_input_temp;
    getline(cin, first_multiple_input_temp);

    vector<string> first_multiple_input = split(rtrim(first_multiple_input_temp));

    int n = stoi(first_multiple_input[0]);

    int k = stoi(first_multiple_input[1]);

    string arr_temp_temp;
    getline(cin, arr_temp_temp);

    vector<string> arr_temp = split(rtrim(arr_temp_temp));

    vector<int> arr(n);

    for (int i = 0; i < n; i++)
    {
        int arr_item = stoi(arr_temp[i]);

        arr[i] = arr_item;
    }

    int result = pairs(k, arr);

    fout << result << "\n";

    fout.close();

    return 0;
}

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

    s.erase(
        s.begin(),
        find_if(s.begin(), s.end(), not1(ptr_fun<int, int>(isspace))));

    return s;
}

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

    s.erase(
        find_if(s.rbegin(), s.rend(), not1(ptr_fun<int, int>(isspace))).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;
}