freeCodeCamp/curriculum/challenges/english/blocks/daily-coding-challenges-python/69bc6cb30c1d112a2e110a06.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
69bc6cb30c1d112a2e110a06	Challenge 249: String Math	29	challenge-249

--description--

Given a string with numbers and other characters, perform math on the numbers based on the count of non-digit characters between the numbers.

• If the count of characters separating two numbers is even, use addition.
• If it's odd, use subtraction.
• Consecutive digits form a single number.
• Operations are applied left to right.
• Ignore leading and trailing characters that aren't digits.

For example, given "3ab10c8", return 5. Add 3 and 10 to get 13 because there's an even number of characters between them. Then subtract 8 from 13 because there's an odd number of characters between the result and 8.

--hints--

do_math("3ab10c8") should return 5.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(do_math("3ab10c8"), 5)`)
}})

do_math("6MINUS4") should return 2.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(do_math("6MINUS4"), 2)`)
}})

do_math("9plus3") should return 12.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(do_math("9plus3"), 12)`)
}})

do_math("5fkwo#10i#%.<>15P=@20!#B/25") should return 15.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(do_math("5fkwo#10i#%.<>15P=@20!#B/25"), 15)`)
}})

do_math("a.67,1$lk6ldf34@#LD@]2d32d2'2l3,@l3L#@2gh35s09if=df#$t9sm49t0df3$^%[vc;:0:4mt") should return 67.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(do_math("a.67,1$lk6ldf34@#LD@]2d32d2'2l3,@l3L#@2gh35s09if=df#$t9sm49t0df3$^%[vc;:0:4mt"), 67)`)
}})

--seed--

--seed-contents--

def do_math(s):

    return s

--solutions--

import re

def do_math(s):
    tokens = re.findall(r'\d+|\D+', s)
    result = None
    pending_op = None
    for token in tokens:
        if re.match(r'^\d+$', token):
            if result is None:
                result = int(token)
            elif pending_op == 'add':
                result += int(token)
            else:
                result -= int(token)
        else:
            pending_op = 'add' if len(token) % 2 == 0 else 'subtract'
    return result