Multiset （权值线段树模版）

#include <algorithm>
#include <string>
#include <cstring>
#include <vector>
#include <map>
#include <stack>
#include <set>
#include <queue>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <ctime>
#include <bitset>
#include <cmath>
#include <sstream>
#include <iostream>
#include <unordered_map>

#define ll long long
#define ull unsigned long long
#define ls nod<<1
#define rs (nod<<1)+1
#define pii pair<int,int>
#define mp make_pair
#define pb push_back
#define INF 0x3f3f3f3f3f3f3f3f
#define max(a, b) (a>b?a:b)
#define min(a, b) (a<b?a:b)


const double eps = 1e-10;
const int maxn = 1e6 + 10;
const ll MOD = 99999999999999;

int sgn(double a) { return a < -eps ? -1 : a < eps ? 0 : 1; }

using namespace std;

int a[maxn]; 
struct val_segment_tree{
    int val;
}tree[maxn<<2];

void build(int nod,int l,int r) {
    if (l == r) {
        tree[nod].val = a[l];   // 值为 l 的个数
        return;
    }
    int mid = (l + r) >> 1;
    build(nod<<1,l,mid);
    build((nod<<1)+1,mid+1,r);
    tree[nod].val = tree[ls].val + tree[rs].val;
}

void add(int nod,int l,int r,int t,int v) {
    if (l == r) {
        tree[nod].val += v;
        return ;
    }
    int mid = (l + r) >> 1;
    if (t <= mid) {
        add(nod<<1,l,mid,t,v);
    }
    else
        add((nod<<1)+1,mid+1,r,t,v);
    tree[nod].val = tree[nod<<1].val + tree[(nod<<1)+1].val;
}
// 删除区间内第num大
void del(int nod,int l,int r,int num,int v) {
    if (l == r) {
        if (tree[nod].val)
            tree[nod].val -= v;
        return ;
    }
    int mid = (l + r) >> 1;
    if (num > tree[ls].val)
        del(rs,mid+1,r,num-tree[ls].val,v);
    else
        del(ls,l,mid,num,v);
    tree[nod].val = tree[ls].val + tree[rs].val;
}
// 查找区间第num大
int query(int nod,int l,int r,int num) {
    if (l == r) {
        if (tree[nod].val)
            return l;
        return -1; // 不存在
    }
    int mid = (l + r) >> 1;
    if (num <= tree[ls].val)
        return query(ls,l,mid,num);
    else
        return query(rs,mid+1,r,num-tree[ls].val);
}

int find(int nod,int l,int r) {
    if (l == r) {
        if (tree[nod].val)
            return l;
        return 0;
    }
    int mid = (l + r) >> 1;
    if (tree[ls].val)
        return find(ls,l,mid);
    else
        return find(rs,mid+1,r);
}

int main() {
    ios::sync_with_stdio(false);
    int n,q;
    cin >> n >> q;
    for (int i = 1;i <= n;i++) {
        int v;
        cin >> v;
        a[v]++;
    }
    build(1,1,n);
    while (q--) {
        int k;
        cin >> k;
        if (k < 0) {
            k = -k;
            del(1,1,n,k,1);
        }
        else {
            add(1,1,n,k,1);
        }
    }
    cout << find(1,1,n) << endl;
    return 0;
}