LeetCode 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:

• -2^31 <= dividend, divisor <= 2^31 - 1

• divisor != 0

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Solution 1: Use Long

class Solution {
public:
    int divide(int dividend, int divisor) {
        if (dividend == INT_MIN && divisor == -1) {
            return INT_MAX;
        }
        bool positive = true;
        if ((dividend > 0 && divisor < 0) || (dividend < 0 && divisor > 0)) {
            positive = false;
        }

        long new_dividend = abs((long)dividend);
        long new_divisor = abs((long)divisor);
        long result = 0;

        int power = 0;
        while (new_divisor <= (new_dividend >> 1)) {
            new_divisor = new_divisor << 1;
            power++;
        }
        
        while (power >= 0) {
            if (new_dividend >= new_divisor) {
                result += (1 << power);
                new_dividend -= new_divisor;
            }
            power--;
            new_divisor = new_divisor >> 1;
        }
        
        return positive ? result : -result;
    }
};

Solution 2: Don't use Long

class Solution {
public:
    int divide(int dividend, int divisor) {
        if (dividend == INT_MIN) {
            if (divisor == -1) {
                return INT_MAX;
            } 
            if (divisor > 0) {
                return -1 + divide(dividend + divisor, divisor);
            } else {
                return 1 + divide(dividend - divisor, divisor);
            }
        }
        if (divisor == INT_MIN) {
            return dividend == INT_MIN ? 1 : 0;
        }
        bool positive = true;
        if ((dividend > 0 && divisor < 0) || (dividend < 0 && divisor > 0)) {
            positive = false;
        }

        int new_dividend = abs(dividend);
        int new_divisor = abs(divisor);
        int result = 0;

        int power = 0;
        while (new_divisor <= (new_dividend >> 1)) {
            new_divisor = new_divisor << 1;
            power++;
        }
        
        while (power >= 0) {
            if (new_dividend >= new_divisor) {
                result += (1 << power);
                new_dividend -= new_divisor;
            }
            power--;
            new_divisor = new_divisor >> 1;
        }
        
        return positive ? result : -result;
    }
};