title: Sum Fai Aj Pairs Array N Integers
signature: fun sumFaiAjPairsArrayNIntegers(a: ArrayList<Int>, n: Int): Int {
test_code: package main
  
  import kotlin.text.*
  import kotlin.math.*
  
  
  // SOLUTION CODE
  // ===================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE
  // ===================================
  fun validateSolution(actual:Int, expected:Int):Boolean{
    return actual.equals(expected)
  }
  fun driver(a: ArrayList<Int>, n: Int, expected:Int):String {
      try{
        if (validateSolution(PLACEHOLDER_FN_NAME(a, n), expected)) {
                return "PASSED"
        }
        return "FAILED"
      } catch (e: Exception){
        return e::class.simpleName as String
      }
  
  }
  
  fun main() {
      var result: String = ""
      result = driver(arrayListOf(2, 8, 12, 19, 23, 23, 26, 39, 54, 56, 57, 57, 73, 78, 83, 83, 89, 91), 15, 3278)
      println("TEST-0...${result}")
      
      result = driver(arrayListOf(62, -34, 10, -28, -42, -12, 4, 20, -20, -84, -76, -16, -44, 26, -78, -40, 50, -10, -56, 76, -88, 24, 64, 10, 64, -8, -68, -42, 26, 24, 62, 36, -68, 8, -68, -2, 8, 38, -18), 20, -112)
      println("TEST-1...${result}")
      
      result = driver(arrayListOf(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1), 18, 0)
      println("TEST-2...${result}")
      
      result = driver(arrayListOf(23, 14, 44, 29, 93, 56, 22, 29, 97, 71, 43, 72, 74, 8, 92, 40, 18, 34, 78, 79, 93, 63, 79, 44, 35, 72, 88, 83, 40, 89, 66, 66, 54, 56, 44, 62, 72, 94, 79, 79, 24, 55, 72, 37, 27, 55, 16, 58, 83), 25, 2551)
      println("TEST-3...${result}")
      
      result = driver(arrayListOf(-96, -94, -90, -90, -86, -82, -80, -80, -58, -48, -40, -32, -32, -20, -20, -20, -12, -12, -6, -6, -2, 0, 4, 16, 16, 16, 42, 48, 58, 64, 68, 76, 76, 76, 78, 80, 82, 88, 88, 88, 92, 94, 96, 98), 27, 16640)
      println("TEST-4...${result}")
      
      result = driver(arrayListOf(1, 1, 1, 1, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 1, 1), 34, 0)
      println("TEST-5...${result}")
      
      result = driver(arrayListOf(3, 4, 4, 8, 10, 10, 11, 15, 19, 19, 20, 24, 25, 25, 27, 30, 41, 43, 44, 45, 47, 55, 59, 59, 61, 63, 63, 67, 67, 69, 72, 73, 75, 77, 77, 78, 81, 81, 83, 84, 92, 94, 99), 31, 12408)
      println("TEST-6...${result}")
      
      result = driver(arrayListOf(94, -86, 94, 54, -52, 86, 68, 64, 98, 54, -14, -60, -60, -92, 80, -16, 28, 16, -74, 68, 32, -54, 58, -16, -2, -52, -92, -36, 96, -18, 14, 76, 16), 26, -6856)
      println("TEST-7...${result}")
      
      result = driver(arrayListOf(0, 0, 0, 0, 1, 1, 1, 1), 7, 0)
      println("TEST-8...${result}")
      
      result = driver(arrayListOf(10, 28, 63, 2, 78, 12, 51, 82, 89, 65, 99), 8, 542)
      println("TEST-9...${result}")
      
          
  }
  
  main()
source_py: def sum_fai_aj_pairs_array_n_integers(a, n):
      cnt = dict()
      ans = 0
      pre_sum = 0
      for i in range(n):
          ans += ((i * a[i]) - pre_sum)
          pre_sum += a[i]
          if ((a[i] - 1) in cnt):
              ans -= cnt[(a[i] - 1)]
          if ((a[i] + 1) in cnt):
              ans += cnt[(a[i] + 1)]
          if (a[i] not in cnt):
              cnt[a[i]] = 0
          cnt[a[i]] += 1
      return ans
source_cpp: int sum_fai_aj_pairs_array_n_integers(vector<int> a, int n) {
    unordered_map < int, int > cnt;
    int ans = 0, pre_sum = 0;
    for ( int i = 0;
    i < n;
    i ++ ) {
      ans += ( i * a [ i ] ) - pre_sum;
      pre_sum += a [ i ];
      if ( cnt [ a [ i ] - 1 ] ) ans -= cnt [ a [ i ] - 1 ];
      if ( cnt [ a [ i ] + 1 ] ) ans += cnt [ a [ i ] + 1 ];
      cnt [ a [ i ] ] ++;
    }
    return ans;
  }