poj2892

树状数组+二分

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
using namespace std;

#define maxn 50005

int n, m;
char st[5];
int ar[maxn];
bool vis[maxn];
int stk[maxn];
int top;

int lowb(int t)
{
    return t &(-t);
}

void add(int i, int v)
{
    for (; i < maxn; ar[i] += v, i += lowb(i));
}

int sum(int i)
{
    int s = 0;
    for (; i > 0; s += ar[i], i -= lowb(i));
    return s;
}

int binarysearch(int a)
{
    int l = 1;
    int r = n + 2;
    while (l < r)
    {
        int mid = (l + r) / 2;
        if (sum(mid) >= a)
            r = mid;
        else
            l = mid + 1;
    }
    return l;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    memset(vis, 0, sizeof(vis));
    scanf("%d%d", &n, &m);
    add(1, 1);
    while (m--)
    {
        int a;
        scanf("%s", st);
        if (st[0] == 'D')
        {
            scanf("%d", &a);
            a++;
            stk[top++] = a;
            vis[a] = true;
            add(a, 1);
        }else if (st[0] == 'R')
        {
            a = stk[--top];
            vis[a] = false;
            add(a, -1);
        }else
        {
            scanf("%d", &a);
            a++;
            if (vis[a])
            {
                printf("0\n");
                continue;
            }
            a = sum(a);
            int s = binarysearch(a);
            int e = binarysearch(a + 1);
            printf("%d\n", e - s - 1);
        }
    }
    return 0;
}