2018 蓝桥杯省赛 B 组模拟赛（一）青出于蓝胜于蓝

题面：https://nanti.jisuanke.com/t/20690

用后序遍历可得到一个序列，问题就转为在(最左子节点...其他节点...根)这个区间中寻找比根小的节点树，再通过树状数组从小到大的顺序依次加入节点，维护区间和。

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<string>
#include<algorithm>
#include<iostream>
#include<queue>
#include<map>
#include<cmath>
#include<set>
#include<stack>
#define ll long long
#define pb push_back
#define max(x,y) ((x)>(y)?(x):(y))
#define min(x,y) ((x)>(y)?(y):(x))
#define cls(name,x) memset(name,x,sizeof(name))
#define fs first
#define sc second
#define mp make_pair
#define L(x) (1<<x)
#define next Next
#define index Index
using namespace std;
const int inf=1e9+10;
const ll llinf=1e17+10;
const int maxn=1e5+10;
const int maxm=25e2+10;
const int mod=1e9+7;
int n,p;
int index;
int key[maxn];
vector<int> V[maxn];
int range[maxn];
int tree[maxn];
int dfs(int now,int fa)
{
    int c=1;
    for(int i=0;i<V[now].size();i++)
        if(V[now][i]!=fa)
        {
            c+=dfs(V[now][i],now);
        }
    key[++index]=now;
    return range[now]=c;
}
int lowbit(int x){return x&(-x);}
void TreeAdd(int pos,int val)
{
    while(pos<=n)
    {
        tree[pos]+=val;
        pos+=lowbit(pos);
    }
}
int Treesum(int r)
{
    int ans=0;
    while(r>0)
    {
        ans+=tree[r];
        r=r-lowbit(r);
    }
    return ans;
}
int TreeQuery(int l,int r)//返回[l,r]总和
{
    return Treesum(r)-Treesum(l-1);
}
int main()
{
    //freopen("in.txt","r",stdin);
    while(~scanf("%d %d",&n,&p))
    {
        cls(tree,0);
        index=0;
        for(int i=1;i<=n-1;i++)
        {
            int u,v;
            scanf("%d %d",&u,&v);
            V[u].pb(v);
            V[v].pb(u);
        }
        dfs(p,-1);
        pair<int,int> point[maxn];
        for(int i=1;i<=n;i++)
            point[i]=mp(key[i],i);
        sort(point+1,point+1+n);
        int ans[maxn];
        for(int i=1;i<=n;i++)
        {
            int id=point[i].fs;
            int pos=point[i].sc;
            ans[id]=TreeQuery(pos+1-range[id],pos);
            TreeAdd(pos,1);
            //printf("[%d %d]",pos+1-range[id],pos);
        }
        for(int i=1;i<=n;i++)
            printf("%d%s",ans[i],i==n?"\n":" ");
    }
	return 0;
}