URAL 1260 Nudnik Photographer DFS DP

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：这个题可以先dfs深搜下，规律dp

dfs：

 #include <bits/stdc++.h>
 using namespace std;
 #define S second
 typedef long long ll;
 const int INF = 0x3f3f3f3f;
 const int M = 1e5+;

 int s;
 int cnt = ;
 bool vis[];
 void dfs( int last, int num )   {
     if( num == s )  {
         cnt++;
         return ;
     }
     for( int i=; i<s+; i++ )
         if( abs(last-i)<= && !vis[i] ) {
             vis[i] = true;
             dfs( i, num+ );
             vis[i] = false;
         }
 }
 int main()  {
     while( ~scanf("%d", &s ) )   {
         memset( vis, false, sizeof(vis) );
         cnt = ;
         vis[] = true;
         dfs( ,  );
         printf("%d\n", cnt );
     }
     return ;
 }

DP：

 #include <bits/stdc++.h>
 using namespace std;
 #define F first
 #define S second
 typedef unsigned long long ll;
 const int INF = 0x3f3f3f3f;
 const int M = 1e5+;

 int s;
 ll dp[];
 void pre()  {
     memset( dp, , sizeof(dp) );
     dp[] = ;
     dp[] = ;
     dp[] = ;
     dp[] = ;
     for( int i=; i<=; i++ )
         dp[i] = dp[i-]+dp[i-]+;
 }
 int main()  {
     pre();
     while( ~scanf("%d", &s ) )   {
         printf("%I64d\n", dp[s] );
     }
     return ;
 }