title: Count Index Pairs Equal Elements Array 1
signature: class Solution {
  
      public int CountIndexPairsEqualElementsArray1(List<int> arr, int n) {
test_code: using System;
  using System.Numerics;
  using System.Diagnostics;
  using System.Collections.Generic;
  using System.Linq;
  using System.Text;
  using System.Security.Cryptography;
  using System.Web.UI;
  using System.Web.Script.Serialization;
  
  // SOLUTION CODE
  // ============================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE 
  // ============================================
  namespace EvaluatePrediction {
      class TestRunner {
          public bool ValidateSolution(int actual, int expected){
              return new JavaScriptSerializer().Serialize(actual) == new JavaScriptSerializer().Serialize(expected);
          }
  
          public string driver(List<int> arr, int n, int expected){
              try{
                PLACEHOLDER_CLS_NAME solution_cls = new PLACEHOLDER_CLS_NAME();
                int pred_result = solution_cls.PLACEHOLDER_FN_NAME(arr, n); 
                if (ValidateSolution(
                      pred_result,
                      expected)){
                  return "PASSED";
                }
                return "FAILED";
              } 
              catch (Exception exception_obj)
              {
                return exception_obj.GetType().FullName;
              }
          }
          static void Main(string[] args) {
              TestRunner runner = new TestRunner();
              String result;
              result = runner.driver(
                  new List<int>{5, 11, 18, 22, 40, 46, 50, 51, 53, 55, 64, 67, 73, 78, 86}, 14, 
                  0
              );
              Console.WriteLine(string.Format(
                  "TEST-0...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{14, -98, 98, 58, -82, 90, -80, -56, -30, -36, -56, -30, -58, 68, 72, -76, 38, -90, -72, 4, -32, 32, -28, 2, 12, -72, 54, 2, 0, -74, 8, 12, 46, 72, -84, -66, 70, 18, 26, 72, -26, 44, -8, 20, -32, -56, 28}, 24, 
                  2
              );
              Console.WriteLine(string.Format(
                  "TEST-1...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1}, 13, 
                  56
              );
              Console.WriteLine(string.Format(
                  "TEST-2...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{93, 23, 62, 64, 31, 78, 99}, 4, 
                  0
              );
              Console.WriteLine(string.Format(
                  "TEST-3...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{-94, -94, -92, -86, -84, -76, -76, -68, -66, -56, -56, -54, -50, -46, -38, -34, -34, -30, -26, -18, -16, 2, 8, 42, 52, 54, 56, 64, 68, 82, 82, 82, 94, 96, 98}, 19, 
                  4
              );
              Console.WriteLine(string.Format(
                  "TEST-4...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{0}, 0, 
                  0
              );
              Console.WriteLine(string.Format(
                  "TEST-5...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{3, 18, 18, 20, 21, 23, 24, 27, 35, 36, 38, 40, 46, 50, 50, 51, 52, 53, 59, 61, 63, 63, 65, 66, 68, 68, 70, 71, 74, 75, 96, 98}, 19, 
                  2
              );
              Console.WriteLine(string.Format(
                  "TEST-6...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{-68, 40, 16, 50, 36, 42, -20, -46, -92, 4, -18, -12, 48, 0, -46, 64, -74, -50, 42, 44, -56, 28, -10, 78, 62, 70, -60, 12, -44, -78}, 23, 
                  2
              );
              Console.WriteLine(string.Format(
                  "TEST-7...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1}, 30, 
                  211
              );
              Console.WriteLine(string.Format(
                  "TEST-8...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{31, 5}, 1, 
                  0
              );
              Console.WriteLine(string.Format(
                  "TEST-9...{0}",
                  result)
              );
          }
      }
  }
  
source_py: def count_index_pairs_equal_elements_array_1(arr, n):
      mp = dict()
      for i in range(n):
          if (arr[i] in mp.keys()):
              mp[arr[i]] += 1
          else:
              mp[arr[i]] = 1
      ans = 0
      for it in mp:
          count = mp[it]
          ans += ((count * (count - 1)) // 2)
      return ans
source_cpp: int count_index_pairs_equal_elements_array_1(vector<int> arr, int n) {
    unordered_map < int, int > mp;
    for ( int i = 0;
    i < n;
    i ++ ) mp [ arr [ i ] ] ++;
    int ans = 0;
    for ( auto it = mp . begin ( );
    it != mp . end ( );
    it ++ ) {
      int count = it -> second;
      ans += ( count * ( count - 1 ) ) / 2;
    }
    return ans;
  }