title: Sum Fai Aj Pairs Array N Integers
signature: func sumFaiAjPairsArrayNIntegers(a []int, n int) int {
test_code: package main
  
  import (
      "fmt"
      "reflect"
      "math"
      "sort"
  )
  
  // SOLUTION CODE
  // ===================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE
  // ===================================
  func validateSolution(actual int, expected int) bool {
      return reflect.DeepEqual(actual,expected)
  }
  
  func driver(a []int, n int, expected int) string {
      if validateSolution(PLACEHOLDER_FN_NAME(a, n),expected) {
              return "PASSED"
      }
      return "FAILED"
  
  }
  
  func main() {
  
      // Use imports to avoid undefined errors
      var _ = reflect.DeepEqual
      _ = math.Abs
      _ = sort.Sort
      result := ""
      result = driver([]int{2, 8, 12, 19, 23, 23, 26, 39, 54, 56, 57, 57, 73, 78, 83, 83, 89, 91}, 
  	15, 3278)
      fmt.Printf("TEST-0...%s\n", result)
      
      result = driver([]int{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)
      fmt.Printf("TEST-1...%s\n", result)
      
      result = driver([]int{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)
      fmt.Printf("TEST-2...%s\n", result)
      
      result = driver([]int{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)
      fmt.Printf("TEST-3...%s\n", result)
      
      result = driver([]int{-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)
      fmt.Printf("TEST-4...%s\n", result)
      
      result = driver([]int{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)
      fmt.Printf("TEST-5...%s\n", result)
      
      result = driver([]int{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)
      fmt.Printf("TEST-6...%s\n", result)
      
      result = driver([]int{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)
      fmt.Printf("TEST-7...%s\n", result)
      
      result = driver([]int{0, 0, 0, 0, 1, 1, 1, 1}, 
  	7, 0)
      fmt.Printf("TEST-8...%s\n", result)
      
      result = driver([]int{10, 28, 63, 2, 78, 12, 51, 82, 89, 65, 99}, 
  	8, 542)
      fmt.Printf("TEST-9...%s\n", result)
      
          
  }
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;
  }