4299: Codechef FRBSUM

4299: Codechef FRBSUM

https://www.lydsy.com/JudgeOnline/problem.php?id=4299

分析：

　　主席树。

　　https://blog.sengxian.com/solutions/bzoj-4408

代码：

 #include<cstdio>
 #include<algorithm>
 #include<cstring>
 #include<cmath>
 #include<iostream>
 #include<cctype>
 using namespace std;
 typedef long long LL;

 inline int read() {
     int x=,f=;char ch=getchar();for(;!isdigit(ch);ch=getchar())if(ch=='-')f=-;
     for(;isdigit(ch);ch=getchar())x=x*+ch-'';return x*f;
 }

 const int N = ;

 int ls[N*], rs[N*], sum[N*], Root[N], CntNode;

 void update(int l,int r,int &rt,int last,int p) {
     rt = ++CntNode;
     sum[rt] = sum[last] + p;
     if (l == r) return;
     int mid = (l + r) >> ;
     if (p <= mid) {
         rs[rt] = rs[last];
         update(l, mid, ls[rt], ls[last], p);
     }
     else {
         ls[rt] = ls[last];
         update(mid+, r, rs[rt], rs[last], p);
     }
 }
 int query(int l,int r,int Head,int Tail,int x) {
     if (l == r) {
         return sum[Tail] - sum[Head];
     }
     int mid = (l + r) >> ;
     if (x <= mid) return query(l, mid, ls[Head], ls[Tail], x);
     else return sum[ls[Tail]] - sum[ls[Head]] + query(mid+, r, rs[Head], rs[Tail], x);
 }
 int main () {

     int n = read();
     for (int i=; i<=n; ++i) {
         int x = read();
         update(, 1e9, Root[i], Root[i-], x);
     }
     int m = read();
     while (m -- ) {
         int l = read(), r = read(), ans = , tmp;
         while (true) {
             tmp = query(, 1e9, Root[l-], Root[r], ans);
             if (tmp < ans) break;
             ans = tmp + ;
         }
         printf("%d\n",ans);
     }
     return ;
 }