洛谷 - P2617 Dynamic Rankings （树状数组套线段树）

传送门：洛谷 - P2617

思路分析

同样是利用差分的性质，对于树状数组的每一个节点建立一颗权值线段树

AC代码

#include <bits/stdc++.h>
#define fi first
#define se second
#define ll long long
#define pb push_back
#define mp make_pair
#define fun function
#define sz(x) (x).size()
#define lowbit(x) (x)&(-x)
#define all(x) (x).begin(),(x).end()
#define mem(a,b) memset(a,b,sizeof(a))

namespace FastIO {
#define BUF_SIZE 100000
#define OUT_SIZE 100000
    bool IOerror=0;
    inline char nc() {
        static char buf[BUF_SIZE],*p1=buf+BUF_SIZE,*pend=buf+BUF_SIZE;
        if(p1==pend) {
            p1=buf;
            pend=buf+fread(buf,1,BUF_SIZE,stdin);
            if(pend==p1) {
                IOerror=1;
                return -1;
            }
        }
        return *p1++;
    }
    inline bool blank(char ch) {
        return ch==' '||ch=='\n'||ch=='\r'||ch=='\t';
    }
    template<class T> inline bool read(T &x) {
        bool sign=0;
        char ch=nc();
        x=0;
        for(; blank(ch); ch=nc());
        if(IOerror)return false;
        if(ch=='-')sign=1,ch=nc();
        for(; ch>='0'&&ch<='9'; ch=nc())x=x*10+ch-'0';
        if(sign)x=-x;
        return true;
    }
    template<class T,class... U>bool read(T& h,U&... t) {
        return read(h)&&read(t...);
    }
#undef OUT_SIZE
#undef BUF_SIZE
};
using namespace std;
using namespace FastIO;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

const int INF = 0x3f3f3f3f;
const int N = 1e5+10;

struct node{
    int sum,l,r;
}tree[N*400];

struct question{
    int op,l,r,k,x,y;
}q[N];

int cnt,root[N],a[N],tot;
int len[2],tmp[2][N];
vector<int>v;

int getid(int x){
    return lower_bound(all(v),x)-v.begin()+1;
}
#define ls tree[x].l
#define rs tree[x].r
void modify(int &x,int l,int r,int val,int k){
    if(!x) x=++cnt;
    tree[x].sum+=k;
    if(l==r) return ;
    int mid = l+r>>1;
    if(val<=mid) modify(ls,l,mid,val,k);
    else modify(rs,mid+1,r,val,k);
}

void add(int x,int k){
    int val = getid(a[x]);
    for(int i=x;i<N;i+=lowbit(i)) modify(root[i],1,tot,val,k);
}

int query(int l,int r,int k){
    if(l==r) return v[l-1];
    
    int sum = 0;
    for(int i=1;i<=len[1];i++) sum+=tree[tree[tmp[1][i]].l].sum;   
    for(int i=1;i<=len[0];i++) sum-=tree[tree[tmp[0][i]].l].sum;
    
    int mid = l+r>>1;
    if(sum>=k){
        for(int i=1;i<=len[0];i++) tmp[0][i] = tree[tmp[0][i]].l;
        for(int i=1;i<=len[1];i++) tmp[1][i] = tree[tmp[1][i]].l;
        return query(l,mid,k);
    } else{
        for(int i=1;i<=len[0];i++) tmp[0][i] = tree[tmp[0][i]].r;
        for(int i=1;i<=len[1];i++) tmp[1][i] = tree[tmp[1][i]].r;
        return query(mid+1,r,k-sum);
    }
}

int get(int l,int r,int k){
    len[0] = len[1] = 0;
    for(int i=(l-1);i;i-=lowbit(i)) tmp[0][++len[0]] = root[i];
    for(int i=r;i;i-=lowbit(i)) tmp[1][++len[1]] = root[i];
    return query(1,tot,k);
}

int main() {

#ifdef xiaofan
    freopen("1.in","r",stdin);
    freopen("1.out","w",stdout);
#endif

    int n,m;
    cin>>n>>m;
    for(int i=1;i<=n;i++) cin>>a[i],v.pb(a[i]);
    for(int i=1;i<=m;i++){
        char op;
        cin>>op;
        q[i].op = (op=='Q');
        if(op=='Q') {
            cin>>q[i].l>>q[i].r>>q[i].k;
        }else{
            cin>>q[i].x>>q[i].y;
            v.pb(q[i].y);
        }
    }
    sort(all(v));
    v.erase(unique(all(v)),v.end());
    tot = sz(v);
    
    for(int i=1;i<=n;i++) add(i,1);

    for(int i=1;i<=m;i++){
        if(q[i].op){
            cout<<get(q[i].l,q[i].r,q[i].k)<<endl;
        }else{
            add(q[i].x,-1);
            a[q[i].x]=q[i].y;
            add(q[i].x,1);
        }
    }




    return 0;
}