主席树套树状数组 动态区间第k小

先打上代码以后更新解释

 #include <cstdio>
 #include <iostream>
 #include <algorithm>
 #include <cstring>
 #include <cmath>
 #define REP(i, s, n) for(int i = s; i <= n; i ++)
 #define RAP(i, n, s) for(int i = n; i >= s; i --)
 #define LOW for(; x; x -= x & (-x))
 using namespace std;
 const int maxn =  + ;
 const int Maxn = ;
 const int maxnode =  * maxn;
 int s[maxnode], ls[maxnode], rs[maxnode], A[maxn], root[maxn], Ln, Rn, L[maxn], R[maxn], c[maxn];
 int n, Q, ms = ;
 void update(int x, int& y, int L, int R, int pos, int v){
     s[y = ++ ms] = s[x] + v;
     if(L == R) return ;
     int M = L + R >> ;
     ls[y] = ls[x]; rs[y] = rs[x];
     if(pos <= M) update(ls[x], ls[y], L, M, pos, v);
     else update(rs[x], rs[y], M + , R, pos, v);
     return ;
 }
 void update(int x, int v){
     for(int i = x; i <= Maxn; i += i & (-i)) update(c[i], c[i], , Maxn, A[x], -); A[x] = v;
     for(int i = x; i <= Maxn; i += i & (-i)) update(c[i], c[i], , Maxn, A[x], ); return ;
 }
 void init(int x, int tp){
     if(!tp) { L[++ Ln] = root[x]; LOW if(c[x]) L[++ Ln] = c[x]; }
     else { R[++ Rn] = root[x]; LOW if(c[x]) R[++ Rn] = c[x]; }
     return ;
 }
 int query(int ql, int qr, int k){
     Ln = Rn = ; init(qr, ); init(ql - , );//0是左
     int ll = , rr = Maxn;
     while(ll < rr){
         int Lsum = , Rsum = , M = ll + rr >> ;
         REP(i, , Ln) Lsum += s[ls[L[i]]];
         REP(i, , Rn) Rsum += s[ls[R[i]]];
         int kth = Rsum - Lsum;
         if(kth >= k){//往左找
             REP(i, , Ln) L[i] = ls[L[i]];
             REP(i, , Rn) R[i] = ls[R[i]];
             rr = M;
         }
         else{//往右找
             REP(i, , Ln) L[i] = rs[L[i]];
             REP(i, , Rn) R[i] = rs[R[i]];
             ll = M + ; k -= kth; //看好了二分！ 别忘了还要减 Σ( ° △ °|||)︴
         }
     }
     return ll;
 }
 inline void read(int &x){
     x = ; int sig = ; char ch = getchar();
     while(!isdigit(ch)) { if(ch == '-') sig = -; ch = getchar(); }
     while(isdigit(ch)) x =  * x + ch - '', ch = getchar();
     x *= sig; return ;
 }
 inline void write(int x){
     if(x == ) { putchar(''); return ; }
     if(x < ) putchar('-'), x = -x;
     int len = , buf[];
     while(x) buf[len ++] = x % , x /= ;
     RAP(i, len - , ) putchar(buf[i] + ''); return ;
 }
 void init(){
     read(n); read(Q);
     REP(i, , n) read(A[i]);
     REP(i, , n) update(root[i - ], root[i], , Maxn, A[i], );
     return ;
 }
 void work(){
     int tp, ql, qr, k, x, v;
     while(Q --){
         read(tp);
         if(tp) read(ql), read(qr), read(k), write(query(ql, qr, k) - ), putchar('\n');// 减一
         else read(x), read(v), update(x, v);
     }
     return ;
 }
 void print(){

     return ;
 }
 int main(){
     init();
     work();
     print();
     return ;
 }

逗比版：

 #include<iostream>
 #include<cstdio>
 #include<cmath>
 #include<algorithm>
 #define t node[d]
 #define cnt countn[d]
 #define repnode(d) for(int i=1;i<=countn[d];i++)
 using namespace std;
 const int maxn=+,maxnode=+,Max=;
 int ls[maxnode],rs[maxnode],s[maxnode],root[maxn],A[maxn],c[maxn],n,m,ms=,countn[],node[][maxn],sum[];
 void update(int x,int& y,int L,int R,int pos,int d){
     s[y=++ms]=s[x]+d;
     if(L==R) return;
     ls[y]=ls[x];rs[y]=rs[x];
     int M=L+R>>;
     if(pos<=M) update(ls[x],ls[y],L,M,pos,d);
     else update(rs[x],rs[y],M+,R,pos,d);
     return;
 }
 void update(int x,int v){
     for(int i=x;i<=Max;i+=i&-i) update(c[i],c[i],,Max,A[x],-);A[x]=v;
     for(int i=x;i<=Max;i+=i&-i) update(c[i],c[i],,Max,A[x],);return;
 }
 void init(int x,int d){
     t[++cnt]=root[x];
     for(;x;x-=x&-x) if(c[x]) t[++cnt]=c[x];
     return;
 }
 int query(int ql,int qr,int k){
     countn[]=countn[]=;
     init(qr,);init(ql-,);
     int L=,R=Max,d;
     while(L<R){
         sum[]=sum[]=;
         int M=L+R>>;
         repnode(d=) sum[d]+=s[ls[t[i]]];
         repnode(d=) sum[d]+=s[ls[t[i]]];
         int kth=sum[]-sum[];
         if(k<=kth){
             repnode(d=) t[i]=ls[t[i]];
             repnode(d=) t[i]=ls[t[i]];
             R=M;
         }
         else{
             repnode(d=) t[i]=rs[t[i]];
             repnode(d=) t[i]=rs[t[i]];
             L=M+;k-=kth;
         }
     } return L;
 }
 inline int read(){
     int x=,sig=;char ch=getchar();
     while(!isdigit(ch)){if(ch=='-') sig=-;ch=getchar();}
     while(isdigit(ch)) x=*x+ch-'',ch=getchar();
     return x*=sig;
 }
 inline void write(int x){
     if(x==){putchar('');return;} if(x<) putchar('-'),x=-x;
     int len=,buf[]; while(x) buf[len++]=x%,x/=;
     for(int i=len-;i>=;i--) putchar(buf[i]+'');return;
 }
 void init(){
     n=read();m=read();
     for(int i=;i<=n;i++) A[i]=read();
     for(int i=;i<=n;i++) update(root[i-],root[i],,Max,A[i],);
     return;
 }
 void work(){
     int tp,i,j,k,x,v;
     while(m--){
         tp=read();
         if(tp){
             i=read();j=read();k=read();
             write(query(i,j,k)-);putchar('\n');
         }
         else{
             x=read();v=read();
             update(x,v);
         }
     }
     return;
 }
 void print(){
     return;
 }
 int main(){
     init();work();print();return ;
 }