【Luogu】P3971Alice And Bob（贪心）

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#include<cctype>
#define maxn 200000
using namespace std;
inline long long read(){
    long long num=0,f=1;
    char ch=getchar();
    while(!isdigit(ch)){
        if(ch==‘-‘)    f=-1;
        ch=getchar();
    }
    while(isdigit(ch)){
        num=num*10+ch-‘0‘;
        ch=getchar();
    }
    return num*f;
}

struct Edge{
    int next,to;
}edge[maxn];
int head[maxn],num;
inline void add(int from,int to){
    edge[++num]=(Edge){head[from],to};
    head[from]=num;
}

int s[maxn];
int dfn[maxn],ID=-1;
int d[maxn];
int q[maxn];

void dfs(int x){
    dfn[x]=++ID;
    for(int i=head[x];i;i=edge[i].next){
        int to=edge[i].to;
        dfs(to);
    }
}

int calc(int lim,int n){
    int now=upper_bound(d+1,d+n+1,lim)-d;
    d[now]=min(d[now],lim);
    return now;
}

int main(){
    memset(d,127,sizeof(d));
    int n=read();
    for(int i=1;i<=n;++i){
        int x=read();
        add(s[x-1],i);
        s[x]=i;
    }
    dfs(0);
    long long ans=0;
    for(int i=n;i>=1;--i)    ans+=calc(dfn[i],n);
    printf("%lld\n",ans);
    return 0;
}