HDU 5792 World is exploding

Test instructions

Gives the length of the sequence of N, followed by the sequence A. Find out that ABCD satisfies ABCD non-equal 1<=a<b<c<d<=n while a[a]<a[b],a[c]>a[d], asking such ABCD there are several.

Idea: First ignore four number 22 unequal condition, that is (, reverse order number) multiply (number of sequential pairs). For example {2,4,1,3}, Reverse is {(2,1), (4,1), (4,3)}, the order is {(2,4), (2,3), (1,3)}, so 3*3=9, a total of nine a<b && c>d four tuples. But there are a lot of illegal, for the number of T, the number of illegal cases is (about T in reverse order number x about the number of pairs of T), minus is the result. (illegal rules can be found by writing a few more groups)

Input:

4

2 4 1 3

4

1 2 3 4

Output:

1

0

Code:

#include <iostream>

#include <cstdio>

#include <cstdlib>

#include <cmath>

#include <vector>

#include <queue>

#include <cstring>

#include <string>

#include <algorithm>

using namespace Std;

typedef long Long LL;

typedef unsigned long long ull;

#define MM (A, B) memset (A,b,sizeof (a));

#define INF 0x7f7f7f7f

#define for (i,n) for (int i=1;i<=n;i++)

#define CT continue;

#define PF printf

#define SC scanf

const int mod=1000000007;

const int N=1E6+10;

int tmp[n],a[n],n,m,c[n],pos[n];

ll Lmin[n],rmin[n],lmax[n],rmax[n];

int lowbit (int i)

{

Return i& (-i);

}

void Add (int x)

{

while (X<=M)

{

C[x]+=1;

X+=lowbit (x);

}

}

int query (int x)

{

int res=0;

while (x>0)

{

RES+=C[X];

X-=lowbit (x);

}

return res;

}

int main ()

{

while (~SCANF ("%d", &n))

{

for (int i=1;i<=n;i++)

{

scanf ("%d", &tmp[i]);

A[i]=tmp[i];

}

Sort (tmp+1,tmp+n+1);//tmp is sorted from small to large, used for tree array to find shun/reverse pairs

M=unique (tmp+1,tmp+n+1)-tmp-1;//de-weight

for (int i=1;i<=n;i++)

Pos[i]=lower_bound (Tmp+1,tmp+m+1,a[i])-tmp;//Find the original number of I in the position after sorting

MM (c,0);

for (int i=1;i<=n;i++)//query 0-i-1 than A[i] small number in lmin[i], between i-m than A[i] put in Lmax

{

Lmin[i]=query (pos[i]-1);//

Lmax[i]=query (M)-query (Pos[i]);

Add (Pos[i]);

}

MM (c,0);

for (int i=n;i>=1;i--)//Reverse One More time

{

Rmin[i]=query (pos[i]-1);

Rmax[i]=query (M)-query (Pos[i]);

Add (Pos[i]);

}

ll ans=0,l=0,r=0;

for (int i=1;i<=n;i++) {r+=rmax[i],l+=lmax[i];};

Ans=l*r;

for (int i=1;i<=n;i++)//Remove illegal

{

Ans-=lmin[i]*rmin[i];

Ans-=lmax[i]*rmax[i];

Ans-=lmax[i]*lmin[i];

Ans-=rmax[i]*rmin[i];

}

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

}

return 0;

}

HDU 5792 World is exploding