1、题目大意：就是给你一个栈，有一些操作，向栈加入空集，把栈顶的元素复制一遍再加入栈，求栈顶两元素的并集，交集

还有栈的第一个元素和栈顶（将栈顶压缩成一个元素）

2、分析：这个其实不是用hash做的，是用系统地一堆函数做的。。

我用hash做的，其实就是暴力的hash，用ULL，用了一堆的STL。。。。不要去重，然后RKhash的长度记得取模

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <vector>
#include <stack>
using namespace std;
#define ULL unsigned long long
#define ygorz pair<ULL, int>
stack<vector<ygorz> > st;
char str[20];
ygorz qaq[200000];
ULL power[200000];
int main() {
    int n;
    scanf("%d", &n);
    power[0] = 1;
    for (int i = 1; i <= 199900; i++) power[i] = power[i - 1] * 107;
    for (int i = 1; i <= n; i++) {
        scanf("%s", str);
        if (str[0] == 'P') {
            vector<ygorz> a;
            a.clear();
            st.push(a);
        }
        else if (str[0] == 'D') {
            st.push(st.top());
        }
        else if (str[0] == 'U') {
            vector<ygorz> a = st.top(); st.pop();
            vector<ygorz> b = st.top(); st.pop();
            int u = 0, v = 0;
            int wt = 0;
            while (u < a.size() || v < b.size()) {
                if (u == a.size()) {
                    qaq[++wt] = b[v];
                    v++;
                }
                else if (v == b.size()) {
                    qaq[++wt] = a[u];
                    u++;
                }
                else {
                    if (a[u] < b[v]) {
                        qaq[++wt] = a[u];
                        u++;
                    }
                    else if (a[u] > b[v]) {
                        qaq[++wt] = b[v];
                        v++;
                    }
                    else {
                        qaq[++wt] = a[u];
                        u++; v++;
                    }
                }
            }
            vector<ygorz> c;
            if(wt){
                c.clear();
                for (int i = 1; i <= wt; i++){
                    c.push_back(qaq[i]);
                }
            }
            st.push(c);
        }
        else if (str[0] == 'I') {
            vector<ygorz> a = st.top(); st.pop();
            vector<ygorz> b = st.top(); st.pop();
            int u = 0, v = 0;
            /*for (; u < a.size(); u++)
            {
                for (; v < b.size()&&b[v] < a[u]; v++);
                if (v < b.size()&&a[u] == b[v]) c.push_back(a[u]);
            }
            */
            int wt = 0;
            while (u < a.size() || v < b.size()) {
                if (u == a.size()) {
                // qaq[++wt] = b[v];
                 v++;
                }
                else if (v == b.size()) {
                // qaq[++wt] = a[u];
                 u++;
                }
                else {
                    if (a[u] < b[v]) {
            //         qaq[++wt] = a[u];
                     u++;
                    }
                    else if (a[u] > b[v]) {
            //         qaq[++wt] = b[v];
                     v++;
                    }
                    else {
                        qaq[++wt] = a[u];
                        u++; v++;
                    }
                }
            }
            vector<ygorz> c;
            if(wt){
                c.clear();
                qaq[wt + 1].first = -1;
                for (int i = 1; i <= wt; i++){
                    c.push_back(qaq[i]);
                }
            }
            st.push(c);
        }
        else {
            ULL hash = 5;
            int ll = 2;
            vector<ygorz> a = st.top(); st.pop();
            vector<ygorz> b = st.top(); st.pop();
            for (int i = 0; i < a.size(); i++) {
                hash = hash * power[a[i].second] + a[i].first;
                ll += a[i].second;
                ll %= 199193;
            }
            hash = hash * power[a.size()] + 7;
            a.clear();
            a.push_back(make_pair(hash, ll));
            int u = 0, v = 0;
            int wt = 0;
            while (u < a.size() || v < b.size()) {
                if (u == a.size()) {
                    qaq[++wt] = b[v];
                    v++;
                }
                else if (v == b.size()) {
                    qaq[++wt] = a[u];
                    u++;
                }
                else {
                    if (a[u] < b[v]) {
                        qaq[++wt] = a[u];
                        u++;
                    }
                    else if (a[u] > b[v]) {
                        qaq[++wt] = b[v];
                        v++;
                    }
                    else {
                        qaq[++wt] = a[u];
                        u++; v++;
                    }
                }
            }
            vector<ygorz> c;
            c.clear();
            c.push_back(qaq[1]);
            for (int i = 2; i <= wt; i++){
                c.push_back(qaq[i]);
            }
            st.push(c);
        }
        printf("%d\n", st.top().size());
    }
    return 0;
}