LUOGU P1503 鬼子进村

#include<iostream>
#include<cstdio>
#include<cstring>
#include<set>

using namespace std;
const int MAXN = 50005;

inline int rd(){
    int x=0,f=1;char ch=getchar();
    while(!isdigit(ch)) {f=ch==‘-‘?0:1;ch=getchar();}
    while(isdigit(ch))  {x=(x<<1)+(x<<3)+ch-‘0‘;ch=getchar();}
    return f?x:-x;
}

int n,m,stk[MAXN],top;
set<int> S;
set<int>::iterator it,it1;

int main(){
    n=rd(),m=rd();char c;int x;
    S.insert(0),S.insert(n+1);
    while(m--){
        c=getchar();
        while(c<‘A‘ || c>‘Z‘) c=getchar();
        if(c==‘R‘) {S.erase(stk[top]);top--;continue;}
        x=rd();
        if(c==‘D‘) S.insert(x),stk[++top]=x;
        else{
            if(S.find(x)!=S.end()) {puts("0");continue;}
            it=S.lower_bound(x);it1=it;it1--;
            printf("%d\n",(*it)-(*it1)-1);
        }
    }
    return 0;
}