BZOJ 2653 middle 二分答案+可持久化线段树

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题目大意：给定一个长度为n的序列，求当子序列s的左端点在[a,b]，右端点在[c,d]时的最大中位数

其中当序列长度为偶数时中位数定义为中间两个数中较大的那个

很难想的一道题具体题解见 http://blog.csdn.net/acm_cxlove/article/details/8566093 说的很详细

区间处理那里 [b,c]是必选的 [a,b)和(c,d]每段取最大加和否则re恒>=0

#include<cstdio>#include<cstring>#include<iostream>#include<algorithm>#define M 20200using namespace std;struct abcd{int lmax,rmax,sum;abcd(int x=0){lmax=rmax=max(x,0);sum=x;}};abcd operator + (const abcd &x,const abcd &y){abcd z;z.sum=x.sum+y.sum;z.lmax=max(x.lmax,x.sum+y.lmax);z.rmax=max(y.rmax,y.sum+x.rmax);return z;}struct Tree{Tree *ls,*rs;abcd seq;}*tree[M],mempool[M*20],*C=mempool;int n,m,ans,a[M];pair<int,int>b[M];Tree* New_Node(Tree *_,Tree *__,abcd ___){C->ls=_;C->rs=__;C->seq=___;return C++;}Tree* Build_Tree(int x,int y){int mid=x+y>>1;if(x==y)return New_Node( 0x0 , 0x0 , abcd(1) );Tree *lson=Build_Tree(x,mid);Tree *rson=Build_Tree(mid+1,y);return New_Node(lson,rson,lson->seq+rson->seq); }Tree *Build_Chain(Tree *p,int x,int y,int z){int mid=x+y>>1;if(x==y)return New_Node( 0x0 , 0x0 , abcd(-1) );if(z<=mid){Tree *lson=Build_Chain(p->ls,x,mid,z);return New_Node(lson,p->rs,lson->seq+p->rs->seq);}else{Tree *rson=Build_Chain(p->rs,mid+1,y,z);return New_Node(p->ls,rson,p->ls->seq+rson->seq);}}abcd Get_Ans(Tree *p,int x,int y,int l,int r){int mid=x+y>>1;if(x==l&&y==r)return p->seq;if(r<=mid) return Get_Ans(p->ls,x,mid,l,r);if(l>mid) return Get_Ans(p->rs,mid+1,y,l,r);return Get_Ans(p->ls,x,mid,l,mid) + Get_Ans(p->rs,mid+1,y,mid+1,r);}bool Judge(int A,int B,int C,int D,int x){int re=0;re+=Get_Ans(tree[x],1,n,B,C).sum;re+=Get_Ans(tree[x],1,n,A,B-1).rmax;re+=Get_Ans(tree[x],1,n,C+1,D).lmax;return re>=0;}int Bisection(int A,int B,int C,int D){int l=1,r=n;while(l+1<r){int mid=l+r>>1;if( Judge(A,B,C,D,mid) )l=mid;elser=mid;}if( Judge(A,B,C,D,r) )return r;return l;}int main(){int i,j,q[10];cin>>n;for(i=1;i<=n;i++)scanf("%d",&b[i].first),b[i].second=i;sort(b+1,b+n+1);for(i=1;i<=n;i++)a[b[i].second]=i;tree[1]=Build_Tree(1,n);for(i=2;i<=n;i++)tree[i]=Build_Chain(tree[i-1],1,n,b[i-1].second);cin>>m;for(i=1;i<=m;i++){for(j=0;j<4;j++)scanf("%d",&q[j]),q[j]=(q[j]+ans)%n+1;sort(q,q+4);printf("%d\n", ans=b[Bisection(q[0],q[1],q[2],q[3])].first );}}

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