这是个经典问题；
用平衡二叉树维护，只不过节点需要多储存一个siz信息，表明在平衡树上的此节点的子节点数；
平衡树稍稍拓展一下的题目，对我而言，写平衡树的代码难度才是关键；
调试了几个小时，这种题目果然需要多练习；
1 #include<iostream> 2 #include<cstring> 3 #include<string> 4 #include<cstdio> 5 #include<cstdlib> 6 #include<algorithm> 7 #include<cmath> 8 #include<ctime> 9 using namespace std; 10 const int maxn=101000; 11 const int inf=100000000; 12 char ch; 13 int n,minn=0,delet=0,x,sum=0,root=0,len=0,all=0; 14 struct node{ 15 int m,v,siz; 16 int ch[2]; 17 int cmp(int x){return m>x?0:1;} 18 }e[maxn<<2]; 19 void countsiz(int &x,int d){ 20 int k=e[x].ch[d]; 21 e[x].siz=e[x].siz-e[k].siz+e[e[k].ch[d^1]].siz; 22 e[k].siz=e[e[k].ch[d]].siz+e[x].siz+1; 23 } 24 void rotate(int &x,int d){ 25 countsiz(x,d); 26 int k=e[x].ch[d]; 27 e[x].ch[d]=e[k].ch[d^1]; 28 e[k].ch[d^1]=x; 29 x=k; 30 } 31 void insert(int &x,int m){ 32 if(x==0){x=++len;e[x].m=m;e[x].v=rand();e[x].siz=1;return;} 33 int d=e[x].cmp(m); 34 insert(e[x].ch[d],m); 35 e[x].siz=e[e[x].ch[0]].siz+e[e[x].ch[1]].siz+1; 36 if(e[e[x].ch[d]].v>e[x].v)rotate(x,d); 37 } 38 void found(int m){ 39 if(m<minn)return; 40 all++; 41 insert(root,m-delet); 42 } 43 void dfs(int &x){ 44 if(x==0)return; 45 if(e[x].m+delet>=minn){dfs(e[x].ch[0]);e[x].siz=e[e[x].ch[0]].siz+e[e[x].ch[1]].siz+1;return;} 46 if(e[x].m+delet<minn){ 47 if(e[x].ch[1]){ 48 rotate(x,1); 49 dfs(x); 50 if(x==0)return; 51 for(int d=0;d<2;d++)if(e[e[x].ch[d]].v>e[x].v)rotate(x,d); 52 e[x].siz=e[e[x].ch[0]].siz+e[e[x].ch[1]].siz+1; 53 } 54 else{ 55 sum+=e[x].siz; 56 x=0; 57 } 58 } 59 } 60 void add(int x){ 61 delet+=x; 62 if(x<0)dfs(root); 63 } 64 int dfs(int x,int k,int right){ 65 int r=e[x].ch[1]; 66 if(x==0)return -inf; 67 if(right+e[r].siz==k)return e[x].m; 68 if(right+e[r].siz>k)return dfs(r,k,right); 69 if(right+e[r].siz<k)return dfs(e[x].ch[0],k,right+e[r].siz+1); 70 } 71 void find(int k){ 72 int p=dfs(root,k-1,0); 73 printf("%d ",p==-inf?-1:p+delet); 74 } 75 void work(){ 76 srand(time(0)); 77 scanf("%d%d",&n,&minn); 78 while(n--){ 79 scanf(" %c %d",&ch,&x); 80 if(ch=='I')found(x); 81 if(ch=='A')add(x); 82 if(ch=='S')add(-x); 83 if(ch=='F')find(x); 84 } 85 cout<<sum<<endl; 86 } 87 int main(){ 88 work(); 89 }