find missing number in array code example

Example 1: find the missing value in an integer array javascript

let a = [5, 7],
  count = 10,
  missing = []

for (let i = 1; i <= count; i++) {
  if (a.indexOf(i) === -1) {
    missing.push(i)
  }
}
console.log(missing)

Example 2: FIND MISSING NUMBER IN AN ARRAY IN PYTHON

def get_missing_summatin(a):
  n = a[-1]
  total = n*(n+1)//2
  summation = 0
  summation = sum(a)
  result = total-summation
  print(result)

a = [1,2,3,5,6,7]
get_missing_summatin(a)