题目链接：hdu_5877_Weak Pair
题意：
给你一棵树，让你找有多少对满足那两个条件的weak pair
题解：
有人用Treap,我不会，然后我用树状数组+离散来替代Treap，用DFS搜到叶子，然后在树状数组中找小于k/a[u]的个数，注意a[u]可以为0,要处理一下
1 #include<bits/stdc++.h> 2 #define F(i,a,b) for(int i=a;i<=b;i++) 3 using namespace std; 4 typedef long long ll; 5 6 const int N=1e5+7; 7 int t,n,v[N],g[N],nxt[N],ed,sum[N],in[N],edn; 8 ll k,a[N],hsh[N],ans; 9 10 inline int getid(ll x){return upper_bound(hsh+1,hsh+1+edn,x)-hsh-1;} 11 inline void add(int x,int c){while(x<=n)sum[x]+=c,x+=x&-x;} 12 inline int ask(int x){int an=0;while(x)an+=sum[x],x-=x&-x;return an;} 13 14 inline void adg(int x,int y){v[++ed]=y,nxt[ed]=g[x],g[x]=ed;} 15 16 void dfs(int u) 17 { 18 add(getid(a[u]),1); 19 for(int i=g[u];i;i=nxt[i])dfs(v[i]); 20 add(getid(a[u]),-1); 21 ll tp; 22 if(a[u]!=0)tp=k/a[u];else tp=hsh[edn]+1; 23 if(tp>hsh[edn])tp=hsh[edn]+1; 24 ans+=ask(getid(tp)); 25 } 26 27 int main() 28 { 29 scanf("%d",&t); 30 while(t--) 31 { 32 scanf("%d%lld",&n,&k); 33 F(i,1,n)scanf("%lld",a+i),hsh[i]=a[i]; 34 sort(hsh+1,hsh+1+n),memset(sum,0,sizeof(sum)); 35 memset(in,0,sizeof(in)),edn=1; 36 memset(g,0,sizeof(g)),ed=0,ans=0; 37 F(i,2,n)if(hsh[i]!=hsh[edn])hsh[++edn]=hsh[i]; 38 F(i,1,n-1) 39 { 40 int x,y; 41 scanf("%d%d",&x,&y); 42 adg(x,y),in[y]++; 43 } 44 F(i,1,n)if(!in[i]){dfs(i);break;} 45 printf("%lld ",ans); 46 } 47 return 0; 48 }