19.1.30 [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.

Example 1:

Input: dividend = 10, divisor = 3
Output: 3

Example 2:

Input: dividend = 7, divisor = -3
Output: -2

Note:

• Both dividend and divisor will be 32-bit signed integers.
• The divisor will never be 0.
• Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231,  231 − 1]. For the purpose of this problem, assume that your function returns 231 − 1 when the division result overflows.

题意

不使用mod或除法来实现除法运算

题解

一开始使用暴力，非常慢，然后用了二分，快了

class Solution {
public:
    int divide(long long dividend, long long divisor) {
        long long s = 0, e = (long long)INT_MAX+1;
        long long res = dividend ^ divisor;
        if (dividend < 0)
            dividend = -dividend;
        if (divisor < 0)
            divisor = -divisor;
        while (s+1<e) {
            long long mid = (s + e) / 2;
            if (mid*divisor <= dividend)
                s = mid;
            else
                e = mid-1;
        }
        if (e*divisor <= dividend)s = e;
        if (res < 0)s = -s;
        if (s > INT_MAX)s = INT_MAX;
        if (s < INT_MIN)s = INT_MIN;
        return s;
    }
};