Codeforces 627 A. XOR Equation (数学)

题目链接：http://codeforces.com/problemset/problem/627/A

题意：

告诉你s 和 x，a + b = s    a xor b = x   a, b > 0。 让你求符合条件的a b有多少对

思路：

a + b = s , a ^ b = x   ==>   s - x = (a & b) * 2

 #include <bits/stdc++.h>
 using namespace std;
 typedef long long LL;
 int a[], b[];
 int main()
 {
     LL s, x;
     cin >> s >> x;
     LL y = s - x;
     if(y %  || x > s) {
         cout <<  << endl;
     } else {
         y /= ;
         int pos1 = , pos2 = , cnt = , fuck = y ? : ;
         for( ; x; ++pos1, x >>= ) {
             if(x & ) {
                 ++cnt;
                 a[pos1] = ;
             }
         }
         for( ; y; ++pos2, y >>= ) {
             if(y & )
                 b[pos2] = ;
         }
         int ok = ;
         for(int i = ; i < max(pos1, pos2); ++i) {
             if(a[i] && b[i]) {
                 ok = ;
                 break;
             }
         }
         if(ok) {
             if(fuck) {
                 cout << (1LL << ((LL)cnt)) << endl;
             } else {
                 cout << (1LL << ((LL)cnt)) -  << endl;
             }
         } else {
             cout <<  << endl;
         }
     }
     return ;
 }