*[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);
}