[leetcode] Divide Two Integers

 1 class Solution
 2 {
 3 public:
 4   int divide(int dividend, int dividor)
 5   {
 6     if(dividend == INT_MIN && dividor == -1)
 7       return INT_MAX;
 8  
 9     auto sign = [=] (int x) -> int { return x>0? 1 : -1;};
10     int p1 = sign(dividend);
11     int p2 = sign(dividor);
12  
13     long long n1 = abs(static_cast<long long>(dividend));
14     long long n2 = abs(static_cast<long long>(dividor));
15  
16     long long ret = 0;
17     long long pre_ret = 0;
18     while(n1 >= n2)
19     {
20       if(ret == 0 && pre_ret == 0)
21       {
22         pre_ret = 1;
23         ret = 1;
24       }
25       else
26       {
27         pre_ret += pre_ret;
28         ret = pre_ret + ret;
29       }
30  
31       n1 -= n2;
32       n2 += n2;
33     }
34  
35     while(n2 >= abs(static_cast<long long>(dividor)) && n1 >= abs(static_cast<long long>(dividor)))
36     {
37       if(pre_ret == 0)
38       {
39         ret += 1;
40         break;
41       }
42  
43       if(n1 < n2)
44       {
45         n2 = n2 >> 1;
46         if(n1 == n2)
47         {
48           ret += pre_ret;
49           break;
50         }
51         pre_ret = pre_ret >> 1;
52       }
53       else
54       {
55         n1 -= n2;
56         n2 = n2 >> 1;
57         if(n1 == n2)
58         {
59           ret += pre_ret;
60           break;
61         }
62         ret = pre_ret + pre_ret + ret;
63         pre_ret = pre_ret >> 1;
64       }
65     }
66  
67     if(p1 == p2)
68       return ret;
69     else
70       return -ret;
71   }
72 };