BZOJ 2212/BZOJ 3702

Posted 2020-08-29 ziliuziliu

线段树合并nlogn.

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 400500
using namespace std;
int n,l[maxn],r[maxn],val[maxn],x,roots,root[maxn];
int ls[maxn*20],rs[maxn*20],sum[maxn*20],tot=0,cnt=0;
long long ans=0,cnt1,cnt2;
int read()
{
    char ch;int data=0;
    while (ch<‘0‘ || ch>‘9‘) ch=getchar();
    while (ch>=‘0‘ && ch<=‘9‘)
    {
        data=data*10+ch-‘0‘;
        ch=getchar();
    }
    return data;
}
void get_tree(int &now)
{
    x=read();
    now=++cnt;val[now]=x;
    if (x) return;
    get_tree(l[now]);
    get_tree(r[now]);

}
void pushup(int now)
{
    sum[now]=sum[ls[now]]+sum[rs[now]];
}
void build(int &now,int left,int right,int val)
{
    now=++tot;
    if (left==right) {sum[now]=1;return;}
    int mid=(left+right)>>1;
    if (val<=mid) build(ls[now],left,mid,val);
    else build(rs[now],mid+1,right,val);
    pushup(now);return;
}
int merge(int x,int y)
{
    if (!x) return y;
    if (!y) return x;
    cnt1+=(long long)sum[rs[x]]*sum[ls[y]];
    cnt2+=(long long)sum[ls[x]]*sum[rs[y]];
    ls[x]=merge(ls[x],ls[y]);
    rs[x]=merge(rs[x],rs[y]);
    pushup(x);
    return x;
}
void dfs(int x)
{
    if (!x) return;
    dfs(l[x]);dfs(r[x]);
    if (!val[x])
    {
        cnt1=cnt2=0;
        root[x]=merge(root[l[x]],root[r[x]]);
        ans+=min(cnt1,cnt2);
    }
    return;
}
int main()
{
    n=read();
    get_tree(roots);
    for (int i=1;i<=cnt;i++)
        if (val[i]) build(root[i],1,n,val[i]);        
    dfs(1);
    printf("%lld\n",ans);
    return 0;
}