笛卡尔树--牛客第四场（sequence）

思路：

O（n）建一颗笛卡尔树，再O（n）dfs向上合并答案就行了。

 #define IOS ios_base::sync_with_stdio(0); cin.tie(0);

 #include <cstdio>//sprintf islower isupper

 #include <cstdlib>//malloc  exit strcat itoa system("cls")

 #include <iostream>//pair

 #include <fstream>

 #include <bitset>

 //#include <map>

 //#include<unordered_map>

 #include <vector>

 #include <stack>

 #include <set>

 #include <string.h>//strstr substr

 #include <string>

 #include <time.h>//srand(((unsigned)time(NULL))); Seed n=rand()%10 - 0~9;

 #include <cmath>

 #include <deque>

 #include <queue>//priority_queue<long long, vector<long long>, greater<long long> > q;//less

 #include <vector>//emplace_back

 //#include <math.h>

 //#include <windows.h>//reverse(a,a+len);// ~ ! ~ ! floor

 #include <algorithm>//sort + unique : sz=unique(b+1,b+n+1)-(b+1);+nth_element(first, nth, last, compare)

 using namespace std;//next_permutation(a+1,a+1+n);//prev_permutation

 #define fo(a,b,c) for(register int a=b;a<=c;++a)

 #define fr(a,b,c) for(register int a=b;a>=c;--a)

 #define mem(a,b) memset(a,b,sizeof(a))

 #define pr printf

 #define sc scanf

 void swapp(long long &a,long long &b);

 double fabss(double a);

 long long maxx(long long a,long long b);

 long long minn(long long a,long long b);

 long long Del_bit_1(long long n);

 long long lowbit(long long n);

 long long abss(long long a);

 const long long INF=(1LL<<);

 const double E=2.718281828;

 const double PI=acos(-1.0);

 const long long inf=(<<);

 const double ESP=1e-;

 const long long mod=(long long)1e9+;

 const long long N=(long long)3e6+;

 int son[N][];

 long long min_[N],max_[N];

 long long a[N];

 long long b[N];

 int stak[N];

 long long ans=-INF;

 void dfs(int rt,int l,int r)

 {

     if(son[rt][])dfs(son[rt][],l,rt-);

     if(son[rt][])dfs(son[rt][],rt+,r);

     long long minl=minn(b[l-],min_[son[rt][]]);

     long long minr=minn(b[rt],min_[son[rt][]]);

     long long maxl=maxx(b[l-],max_[son[rt][]]);

     long long maxr=maxx(b[rt],max_[son[rt][]]);

     max_[rt]=maxx(maxl,maxr);

     min_[rt]=minn(minl,minr);

     ans=maxx(ans,(maxr-minl)*a[rt]);

     ans=maxx(ans,(minr-maxl)*a[rt]);

 }

 int main()

 {

     int n;

     sc("%d",&n);

     fo(i,,n)sc("%lld",&a[i]);

     fo(i,,n)sc("%lld",&b[i]),b[i]+=b[i-];

     long long top=;

     fo(i,,n)

     {

         while(top&&a[i]<a[stak[top]])

             son[i][]=stak[top--];

         if(top)

             son[stak[top]][]=i;

         stak[++top]=i;

     }

     min_[]=INF,max_[]=-INF;//注意细节;;...

     dfs(stak[],,n);

     pr("%lld\n",ans);

     return ;

 }

 /**************************************************************************************/

 long long maxx(long long a,long long b)

 {

     return a>b?a:b;

 }

 void swapp(long long &a,long long &b)

 {

     a^=b^=a^=b;

 }

 long long lowbit(long long n)

 {

     return n&(-n);

 }

 long long Del_bit_1(long long n)

 {

     return n&(n-);

 }

 long long abss(long long a)

 {

     return a>?a:-a;

 }

 double fabss(double a)

 {

     return a>?a:-a;

 }

 long long minn(long long a,long long b)

 {

     return a<b?a:b;

 }