*[codility]Fish

https://codility.com/demo/take-sample-test/fish

一开始习惯性使用单调栈，后来发现一个普通栈就可以了。

#include <stack>

using namespace std;



int solution(vector<int> &A, vector<int> &B) {

    int size = A.size();

    int deadNum = 0;

    stack<int> stk;

    // downstream

    for (int i = 0; i < size; i++) {

        if (B[i] == 0) {

            bool done = false;

            while (not done) {

                if (!stk.empty()) {

                    int top = stk.top();

                    if (A[top] > A[i]) {

                        deadNum++;

                        done = true;;

                    } else {

                        deadNum++;

                        stk.pop();

                    }

                } else {

                    done = true;   

                }

            }

        } else { // B[i] == 1

            stk.push(i);

        }

    }

    return (size - deadNum);

}