[BZOJ1231] [Usaco2008 Nov]mixup2 混乱的奶牛

传送门

http://www.lydsy.com/JudgeOnline/problem.php?id=1231

题目大意

如果任意相邻两点的值的差大于m那么这种排列是混乱的,询问混乱的排列方式和

题解

状压DP(数据范围小且是关于集合的问题)
dp[i,j]:i表示奶牛的二进制集合,j表示最后一头牛是j
枚举两头在i集合中的奶牛,若差值大于m就转移
(突然发现inc如果不是longint大了会出问题)

var dp:array[0..65540,0..20]of int64; x:array[0..20]of longint; i,j,k:longint; n,m:longint; ans:int64;begin readln(n,m); for i:=1 to n do  readln(x[i]); fillchar(dp,sizeof(dp),0); for i:=1 to n do  dp[1<<(i-1),i]:=1; for i:=1 to (1<<n)-1 do  for j:=1 to n do   if i and(1<<(j-1))<>0   then    for k:=1 to n do     if (i and(1<<(k-1))<>0)and(abs(x[j]-x[k])>m)     then dp[i,j]:=dp[i,j]+dp[i-1<<(j-1),k]; ans:=0; for i:=1 to n do  ans:=ans+dp[1<<n-1,i]; writeln(ans);end.