title: Find The Missing Number 1
signature: func findTheMissingNumber1(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{13, 27, 46, 59, 62, 82, 92}, 
  	6, -261)
      fmt.Printf("TEST-0...%s\n", result)
      
      result = driver([]int{22, 86, -64, -20, -56, -16, 86, 42, 72, -90, 10, 42, 56, 8, 50, 24, -34, 0, -78, 64, 18, 20, -84, -22, 90, -20, 86, 26, -54, 0, 90, -48, 4, 88, 18, -64, -22, -74, 48, -36, -86, -24, 88, -64, 68, 62, 92}, 
  	38, 524)
      fmt.Printf("TEST-1...%s\n", result)
      
      result = driver([]int{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1}, 
  	15, 131)
      fmt.Printf("TEST-2...%s\n", result)
      
      result = driver([]int{55, 89, 56, 85, 26, 4, 91, 91, 3, 77, 63, 59, 76, 90, 1, 94, 44, 70, 8, 54, 3, 91, 29, 95, 28, 75, 20}, 
  	22, -954)
      fmt.Printf("TEST-3...%s\n", result)
      
      result = driver([]int{-94, -84, -80, -78, -66, -62, -54, -52, -26, -8, -8, -6, 4, 4, 8, 14, 26, 58, 60, 62, 62, 76, 78, 86, 92}, 
  	18, 694)
      fmt.Printf("TEST-4...%s\n", result)
      
      result = driver([]int{1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0}, 
  	25, 341)
      fmt.Printf("TEST-5...%s\n", result)
      
      result = driver([]int{1, 2, 7, 7, 9, 14, 23, 29, 31, 31, 35, 35, 38, 41, 44, 49, 49, 50, 51, 54, 55, 56, 57, 63, 67, 69, 73, 79, 79, 80, 86, 88, 93}, 
  	24, -506)
      fmt.Printf("TEST-6...%s\n", result)
      
      result = driver([]int{78, -48, 16, 22, -16, 34, 56, -20, -62, -82, -74, -40, 20, -24, -46, 64, 66, -76, 58, -84, 96, 76, 86, -32, 46}, 
  	12, 227)
      fmt.Printf("TEST-7...%s\n", result)
      
      result = driver([]int{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 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, 1, 1, 1, 1, 1, 1, 1}, 
  	29, 463)
      fmt.Printf("TEST-8...%s\n", result)
      
      result = driver([]int{73, 76, 25, 59, 40, 85, 90, 38, 13, 97, 93, 99, 45, 7}, 
  	12, -697)
      fmt.Printf("TEST-9...%s\n", result)
      
          
  }
source_py: def find_the_missing_number_1(a, n):
      (i, total) = (0, 1)
      for i in range(2, (n + 2)):
          total += i
          total -= a[(i - 2)]
      return total
source_cpp: int find_the_missing_number_1(vector<int> a, int n) {
    int i, total = 1;
    for ( i = 2;
    i <= ( n + 1 );
    i ++ ) {
      total += i;
      total -= a [ i - 2 ];
    }
    return total;
  }