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;
 }