当我看到我的几年前曾经的代码我震惊了，这不是纯暴力吗？竟然直接秒过。

#include <bits/stdc++.h>
#define MAX (50000 + 7)
using namespace std;

int N, M, x, tx, top, S[MAX], use[MAX];
char op[3];

int main()
{
    scanf("%d%d", &N, &M);
    while (M--)
    {
        scanf("%s", op);
        if (op[0] == 'R') use[S[top--]] = 0;
        
        scanf("%d", &x);
        if (op[0] == 'D') use[S[++top] = x] = 1;
        if (op[0] == 'Q')
        {
            int L = 0, R = N + 1;
            for (int i = 1; i <= top; i++)
            {
                if (S[i] <= x) L = L > S[i] ? L : S[i];
                if (S[i] >= x) R = R > S[i] ? S[i] : R;
            }printf("%d\n", L==R ? 0 : R-L-1);
        }
    }
}