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Challenge 237: Equation Validation

curriculum/challenges/english/blocks/daily-coding-challenges-python/69b559d2903b9e4afe9075f7.md

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--description--

Given a string representing a math equation, determine whether it is correct.

  • The left side may contain up to three positive integers and the operators +, -, *, and /.
  • The equation will be given in the format: "number operator number = number" (with two or three numbers on the left). For example: "2 + 2 = 4" or "2 + 3 - 1 = 4".
  • The right side will always be a single integer.

Follow standard order of operations: multiplication and division are evaluated before addition and subtraction, from left-to-right.

--hints--

is_valid_equation("2 + 2 = 4") should return True.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_equation("2 + 2 = 4"), True)`)
}})

is_valid_equation("2 + 3 - 1 = 4") should return True.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_equation("2 + 3 - 1 = 4"), True)`)
}})

is_valid_equation("8 / 2 = 4") should return True.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_equation("8 / 2 = 4"), True)`)
}})

is_valid_equation("10 * 5 = 50") should return True.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_equation("10 * 5 = 50"), True)`)
}})

is_valid_equation("2 - 2 = 0") should return True.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_equation("2 - 2 = 0"), True)`)
}})

is_valid_equation("2 + 9 / 3 = 5") should return True.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_equation("2 + 9 / 3 = 5"), True)`)
}})

is_valid_equation("20 - 2 * 3 = 14") should return True.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_equation("20 - 2 * 3 = 14"), True)`)
}})

is_valid_equation("2 + 5 = 6") should return False.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_equation("2 + 5 = 6"), False)`)
}})

is_valid_equation("10 - 2 * 3 = 24") should return False.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_equation("10 - 2 * 3 = 24"), False)`)
}})

is_valid_equation("3 + 9 / 3 = 4") should return False.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_equation("3 + 9 / 3 = 4"), False)`)
}})

--seed--

--seed-contents--

py
def is_valid_equation(equation):

    return equation

--solutions--

py
def is_valid_equation(equation):
    left, right = equation.split(" = ")
    tokens = left.split(" ")

    i = 1
    while i < len(tokens) - 1:
        op = tokens[i]
        if op in ("*", "/"):
            a = int(tokens[i - 1])
            b = int(tokens[i + 1])
            computed = a * b if op == "*" else a // b
            tokens[i - 1:i + 2] = [str(computed)]
        else:
            i += 2

    result = int(tokens[0])
    i = 1
    while i < len(tokens) - 1:
        op = tokens[i]
        val = int(tokens[i + 1])
        result = result + val if op == "+" else result - val
        i += 2

    return result == int(right)