29-Divide-Two-Integers.md

29. Divide Two Integers

Given two integers dividend and divisor, divide two integers without using multiplication, division, and mod operator.

Return the quotient after dividing dividend by divisor.

The integer division should truncate toward zero, which means losing its fractional part. For example, truncate(8.345) = 8 and truncate(-2.7335) = -2.

Note:

• Assume we are dealing with an environment that could only store integers within the 32-bit signed integer range: [−2³¹, 2³¹ − 1]. For this problem, assume that your function returns 2³¹ − 1 when the division result overflows.

Example 1:

Input: dividend = 10, divisor = 3
Output: 3
Explanation: 10/3 = truncate(3.33333..) = 3.

Example 2:

Input: dividend = 7, divisor = -3
Output: -2
Explanation: 7/-3 = truncate(-2.33333..) = -2.

Example 3:

Input: dividend = 0, divisor = 1
Output: 0

Example 4:

Input: dividend = 1, divisor = 1
Output: 1

Constraints:

• -231 <= dividend, divisor <= 231 - 1
• divisor != 0

Solution

class Solution:
    def divide_by_hand(self, dividend: int, divisor: int) -> (int, int):
        i = 0
        total = 0
        while True:
            if total + divisor > dividend:
                break
            i += 1
            total += divisor
        return (i, dividend - total)
    def divide(self, dividend: int, divisor: int) -> int:
        _overflow = (1<<31) - 1
        if abs(dividend) < abs(divisor):
            return 0
        neg = (dividend < 0 < divisor or divisor < 0 < dividend)
        dividend, divisor = abs(dividend), abs(divisor)
        ans = ''
        str_dividend, str_divisor = str(dividend), str(divisor)
        carry = str(str_dividend[0:len(str_divisor)-1])
        for i in range(len(str_dividend) - len(str_divisor) + 1):
            carry += str_dividend[i+len(str_divisor)-1]
            tmp = self.divide_by_hand(int(carry), divisor)
            ans += str(tmp[0])
            carry = str(tmp[1])
        ans = 0 - int(ans) if neg else int(ans)
        return ans if 0 - (1<<31) <= ans < (1<<31) else _overflow

Go back to when you were in primary school: Long Division.