420B

Solution

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

#define MAX_MSG_NUM 100005
#define MAX_PEOPEL_NUM 100005
#define D(x) 

struct Msg
{
    int id;
    bool on;
}msg[MAX_MSG_NUM];

int people_num, msg_num;
bool vis[MAX_PEOPEL_NUM];
bool wait[MAX_PEOPEL_NUM];
int init_num;
int ans[MAX_PEOPEL_NUM];

void input()
{
    scanf("%d%d", &people_num, &msg_num);
    for (int i = 0; i < msg_num; i++)
    {
        char st[2];
        int a;
        scanf("%s%d", st, &a);
        msg[i].on = (st[0] == '+');
        msg[i].id = a - 1;
    }
}

void make_wait()
{
    memset(vis, 0, sizeof(vis));
    memset(wait, 0, sizeof(wait));
    bool did = false;
    init_num = 0;
    for (int i = 0; i < msg_num; i++)
    {
        if (vis[msg[i].id])
        {
            continue;
        }
        if (!msg[i].on)
        {
            wait[msg[i].id] = true;
            init_num++;
            did = true;
        }
        vis[msg[i].id] = true;
    }
    if (!did)
    {
        wait[msg[0].id] = true;
    }
}

void work()
{
    int on_num = init_num;
    for (int i = 0; i < msg_num; i++)
    {
                D(printf("%d %d\n", i, on_num);)
        if (msg[i].on)
        {
            on_num++;
            if (on_num == 1 && !wait[msg[i].id])
            {
                memset(wait, 0, sizeof(wait));
            }
            continue;
        }
        on_num--;
        if (!wait[msg[i].id])
        {
            continue;
        }
        if (on_num > 0)
        {
            wait[msg[i].id] = false;
        }
    }
}

void output()
{
    int ans_num = 0;
    for (int i = 0; i < people_num; i++)
    {
        if (wait[i] || !vis[i])
        {
            ans[ans_num++] = i + 1;
            D(printf("i = %d\tans = %d\n", i, ans[ans_num - 1]);)
        }
    }
    printf("%d\n", ans_num);
    if (ans_num == 0)
        return;
    printf("%d", ans[0]);
    for (int i = 1; i < ans_num; i++)
    {
        printf(" %d", ans[i]);
    }
    puts("");
}

int main()
{
    input();
    make_wait();
    work();
    output();
    return 0;
}