Divide Two Integers

Divide two integers without using multiplication, division and mod operator.

If it is overflow, return MAX_INT.

任何一个数字都可以表示为num=a_0*2^0+a_1*2^1+a_2*2^2+...+a_n*2^n，

因而可以用移位模拟出发，除数就是a_0+a_1+a_2...的和。

public class Solution {
public static int divide(int dividend, int divisor) {
if(divisor==0) return Integer.MAX_VALUE;
if(divisor==-1 && dividend == Integer.MIN_VALUE)
return Integer.MAX_VALUE;
long pDividend = Math.abs((long)dividend);
long pDivisor = Math.abs((long)divisor);
int result = 0;
while(pDividend>=pDivisor){
//calculate number of left shifts
int numShift = 0;
while(pDividend>=(pDivisor<<numShift))
numShift++;
//dividend minus the largest shifted divisor
result += 1<<(numShift-1);
pDividend -= (pDivisor<<(numShift-1));
}
if((dividend>0 && divisor>0) || (dividend<0 && divisor<0))
return result;
else
return -result;
}
}