# Find The Missing Number

The problem is as follows:
We are given a list of n-1 integers and these integers are in the range of 1 to n.
There are no duplicates in the list. One of the integers is missing in the list.
Give an algorithm to find the missing integer.

Sample Input: [1,2,4,6,3,7,8]
Sample Output: 5

```arr = [1,2,4,6,3,7,8]

'''solution using brute force
Complexity Time: O(n^2) Space = O(1)'''

def findMissing(arr):
missingNumber = -1
for i in range(1,len(arr)):
if i in arr:
pass
else:
missingNumber = i
return missingNumber

print findMissing(arr)

'''solution using sorting
Complexity Time: O(nlogn) Space:O(1)'''

def findMissingUsingSorting(arr):
missingNumber = -1
arr.sort()
for i in range(len(arr)):

if arr[i] == i+1:
pass
else:
missingNumber = i+1
break
return missingNumber

print findMissing(arr)

'''solution using hashing technique
Complexity Time: O(n) Space O(n)'''

def findMissingUsingHashing(arr):
numberDict = {}
missingNumber = -1
for i in range(len(arr)+1):
numberDict[i+1] = 0

for i in arr:
numberDict[i] = 1

for i in numberDict:
if numberDict[i] == 0:
missingNumber = i

return missingNumber

print findMissing(arr)

```