HDU 5151 sit sit sit band DP + permutation combination

Sit sit sit question description

In an XX university there areNN chairs lined up, no one in the chair, each chair coloured, blue or red, respectively. Here we go, then.Nn pupils, numbered in the order of three-,..., N. For each student, he would sit down with a chair that no one was sitting on. But if the chair satisfies the following three conditions, he will not sit. 1. There are two adjacent chairs on both sides of this chair 2. The chairs on the left and right side of the chair are not empty, that is, someone sat down 3. The color of the chair on the left and right side of the chair is different if the current student cannot find a chair to sit on, he will go away. For one of the current students, he may have a choice of chairs to sit on. Your task is to calculate how many different all the students are sitting down in the situation. The result may be large and the output answer is1000000007 ({10}^{9}+7)< Span class= "Mord" >10000 00007  (1 0   ? 9  ?? +7) modulo.  

Enter a description

N (1\leq n\leq)n(1≤n≤100nn integers representing the color of a chair, The number ranges from 0 to 1, 0 for Blue, and 1 for red. 

Output description

For each set of test data, the output answer1000000007 ({10}^{9}+7)< Span class= "Mord" >10000 00007  (1 0   ? 9  ?? +7) modulo.  

Input sample

31 0 041 0 0 1

Output sample

48

Problem : interval dp+ Combinatorial counting problems, the transfer equation is, each time you select the last position of the current interval, and then multiply the combined number c[interval length [left interval length]

Note the initialization of the DP array-1

//Meek///#include <bits/stdc++.h>#include <cstdio>#include<cmath>#include<cstring>#include<algorithm>#include<iostream>#include<bitset>using namespacestd;#defineMem (a) memset (A,0,sizeof (a))#definePB Push_back#defineFi first#defineSe Second#defineMP Make_pairtypedefLong Longll;Const intN = the;Const intM =1000001;Const intINF =0x3f3f3f3f;Const intMOD =1000000007;Const DoubleEPS =0.000001;intdp[n][n],a[n],n,c[n+5][n+5];intDfsintLintr) {if(dp[l][r]!=-1)returnDp[l][r]; if(L > R)return 1; int& ret = Dp[l][r] =0; if(L = =r) {if(L = =1|| r = = n| | a[l-1] = = a[r+1])returnRET =1; Else returnRET =0; }     for(inti=l;i<=r;i++) {ret+ = 1ll*dfs (l,i-1) *dfs (i+1, R)%mod*c[r-l][i-l]%MOD; RET%=MOD; }    returnret;}voidinit () { for(intI=0; i<= -; i++) {c[i][0] =1;  for(intj=1; j<=i;j++) {C[i][j]= (c[i-1][J] + c[i-1][j-1])%MOD; } }}intMain () {init ();  while(SCANF ("%d", &n)!=-1) {memset (DP,-1,sizeof(DP));  for(intI=1; i<=n;i++) scanf ("%d",&A[i]); printf ("%d\n", DFS (1, N)); }    return 0;}

Code

HDU 5151 sit sit sit band DP + permutation combination