# Find the missing value from the given equation a + b = c in Python

Suppose we have one equation in this form: a + b = c, now any one of the terms of a, b or c is missing. We have to find the missing one.

So, if the input is like ? + 4 = 9, then the output will be 5

To solve this, we will follow these steps −

• delete all blank spaces from the string and change (+ and = to comma ',')

• elements := a list of elements by splitting the string separated by comma

• idx := 0

• for i in range 0 to size of elements, do

• if elements[i] is not numeric, then

• idx := i

• come out from the loop

• if last element is missing, then

• return first element + second element

• otherwise when second element is missing, then

• return last element - first element

• otherwise when first element is missing, then

• return last element - second element

## Example

Let us see the following implementation to get better understanding −

Live Demo

def find_missing(string):
string = string.strip().replace(' ', '')
string = string.replace('=',',')
string = string.replace('+',',')
elements = string.split(',')
idx = 0
for i in range(len(elements)):
if not elements[i].isnumeric():
idx = i
break
if idx == 2:
return int(elements) + int(elements)
elif idx == 1:
return int(elements) - int(elements)
elif idx == 0:
return int(elements) - int(elements)

print(find_missing('6 + 8 = ?'))
print(find_missing('? + 8 = 20'))
print(find_missing('5 + ? = 15'))

## Input

'6 + 8 = ?'
'? + 8 = 20'
'5 + ? = 15'

## Output

14
12
10