Fish

// you can use includes, for example:
// #include <algorithm>
#include <stack>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;

int solution(vector<int> &A, vector<int> &B) {
    // write your code in C++14 (g++ 6.2.0)
    
    stack<int> upstream;
    stack<int> downstream;
    for (size_t i = 0; i < A.size(); ++i) {
        if (B[i] == 0) {
            upstream.push(i);
            
            while (downstream.size() > 0) {
                auto down = downstream.top();
                if (A[i] > A[down]) {
                    downstream.pop();
                }
                if (A[i] < A[down]) {
                    upstream.pop();
                    break;
                }
            }
        }  
        else {
            downstream.push(i); 
        }
    }
    
    return upstream.size() + downstream.size();
}