cogs2262 决战前的黎明 CDQ分治

链接：http://cogs.pro:8080/cogs/problem/problem.php?pid=2262

题意：求出三维偏序中顺序对的数量。

虽说打过$CDQ$……但是三个月了又跟没打过有什么区别……不说了……

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <algorithm>
 5 using namespace std;
 6 const int maxn=200005;
 7 struct node
 8 {
 9     int from,to,dis,next;
10 }edge[maxn<<1];
11 int head[maxn],tot;
12 void addedge(int u,int v,int w)
13 {
14     edge[++tot]=(node){u,v,w,head[u]};head[u]=tot;
15 }
16 struct ques
17 {
18     int id,d,val;
19     inline bool operator <(const ques &b)const
20     {
21         if(d!=b.d)return d<b.d;
22         return id<b.id;
23     }
24 }A[maxn],B[maxn];
25 void dfs(int root,int pa)
26 {
27     for(int i=head[root];i;i=edge[i].next)
28     {
29         int v=edge[i].to;
30         if(v!=pa)A[v].d=A[root].d+edge[i].dis,dfs(v,root);
31     }
32 }
33 int n;
34 int C[maxn];
35 int lowbit(int x)
36 {
37     return x&(-x);
38 }
39 void Modify(int pos,int val)
40 {
41     for(;pos<=n;pos+=lowbit(pos))C[pos]+=val;
42 }
43 int Query(int pos)
44 {
45     int res=0;
46     for(;pos;pos-=lowbit(pos))res+=C[pos];
47     return res;
48 }
49 long long ans;
50 void CDQ(int l,int r)
51 {
52     if(l>=r)return;
53     int mid=(l+r)>>1;CDQ(l,mid);CDQ(mid+1,r);
54     int l1=l,l2=mid+1,now=l;
55     while(l1<=mid&&l2<=r)
56         if(A[l1]<A[l2])B[now++]=A[l1++];
57         else B[now++]=A[l2++];
58     while(l1<=mid)B[now++]=A[l1++];
59     while(l2<=r)B[now++]=A[l2++];
60     for(int i=l;i<=r;i++)A[i]=B[i];
61     for(int i=l;i<=r;i++)
62         if(A[i].id<=mid)Modify(A[i].val,1);
63         else ans+=Query(A[i].val);
64     for(int i=l;i<=r;i++)
65         if(A[i].id<=mid)Modify(A[i].val,-1);
66 }
67 int haha()
68 {
69     freopen("ZZ.in","r",stdin);
70     freopen("ZZ.out","w",stdout);
71     scanf("%d",&n);
72     for(int i=1;i<=n;i++)scanf("%d",&A[i].val),A[i].id=i;
73     for(int i=1;i<n;i++)
74     {
75         int x,y,z;scanf("%d%d%d",&x,&y,&z);
76         addedge(x,y,z);addedge(y,x,z);
77     }
78     dfs(1,0);CDQ(1,n);printf("%lld\n",ans);
79 }
80 int sb=haha();
81 int main(){;}
cogs2262

 

posted @ 2017-10-25 20:24  ccc000111  阅读(332)  评论(0)  编辑  收藏  举报