USACO 5.4 Twofive(DP)

非常不容易的一题，思路就是DP之后输出路径。但是此题，路径和DP的方式不一样，路径要按字典序输出。

开始写了一个版本，N 10000的时候就是过不了，后来才发现，自己的写法有问题，无法保证字典序。看了看题解，其实也不是很懂。

终于还有3个题，加油了！！

 /*
 ID: cuizhe
 LANG: C++
 TASK: twofive
 */
 #include <cstdio>
 #include <cstring>
 using namespace std;
 char str[];
 char te[];
 int dp[][][][][];
 int judge(int x,int step)
 {
     if(!te[x]||te[x] == step + 'A')
     return ;
     else
     return ;
 }
 int dfs(int x1,int x2,int x3,int x4,int x5,int step)
 {
     int ans = ;
     if(step == )
     return ;
     if(dp[x1][x2][x3][x4][x5])
     return dp[x1][x2][x3][x4][x5];
     if(x1 < &&judge(x1,step))
     ans += dfs(x1+,x2,x3,x4,x5,step+);
     if(x2 < x1&&judge(x2+,step))
     ans += dfs(x1,x2+,x3,x4,x5,step+);
     if(x3 < x2&&judge(x3+,step))
     ans += dfs(x1,x2,x3+,x4,x5,step+);
     if(x4 < x3&&judge(x4+,step))
     ans += dfs(x1,x2,x3,x4+,x5,step+);
     if(x5 < x4&&judge(x5+,step))
     ans += dfs(x1,x2,x3,x4,x5+,step+);
     return dp[x1][x2][x3][x4][x5] = ans;
 }
 int main()
 {
     char ch[];
     freopen("twofive.in","r",stdin);
     freopen("twofive.out","w",stdout);
     int n,i,temp,ans;
     scanf("%s",ch);
     if(ch[] == 'N')
     {
         scanf("%d",&n);
         for(i = ;i < ;i ++)
         {
             for(te[i] = 'A';;te[i] ++)
             {
                 memset(dp,,sizeof(dp));
                 if((temp = dfs(,,,,,)) < n)
                 n -= temp;
                 else
                 break;
             }
         }
         te[] = '\0';
         printf("%s\n",te);
     }
     else
     {
         scanf("%s",str);
         for(i = ;i < ;i ++)
         {
             for(te[i] = 'A';te[i] < str[i];te[i] ++)
             {
                 memset(dp,,sizeof(dp));
                 ans += dfs(,,,,,);
             }
         }
         printf("%d\n",ans+);
     }
     return ;
 }