递推DP HDOJ 5375 Gray code

题目传送门

 /*
     题意：给一个串，只能是0，1，?(0/1)。计算格雷码方法：当前值与前一个值异或，若为1，可以累加a[i],问最大累加值
     DP：dp[i][0/1]表示当前第i位选择0/1时的最大分数，那么分类讨论，情况太多，看代码，注意不可能的状态不要转移
 */
 /************************************************
 * Author        :Running_Time
 * Created Time  :2015-8-11 15:49:03
 * File Name     :G.cpp
  ************************************************/

 #include <cstdio>
 #include <algorithm>
 #include <iostream>
 #include <sstream>
 #include <cstring>
 #include <cmath>
 #include <string>
 #include <vector>
 #include <queue>
 #include <deque>
 #include <stack>
 #include <list>
 #include <map>
 #include <set>
 #include <bitset>
 #include <cstdlib>
 #include <ctime>
 using namespace std;

 #define lson l, mid, rt << 1
 #define rson mid + 1, r, rt << 1 | 1
 typedef long long ll;
 const int MAXN = 2e5 + ;
 const int INF = 0x3f3f3f3f;
 const int MOD = 1e9 + ;
 char s[MAXN];
 int a[MAXN];
 int dp[MAXN][];

 int work(int n)    {
     memset (dp, , sizeof (dp));
     if (s[] == '?')    dp[][] = a[];
     else    {
         int t = s[] - '';
         if (t == )    dp[][] = a[];
     }
     for (int i=; i<=n; ++i)    {
         if (s[i] == '?')    {
             if (s[i-] == '?')    {
                 dp[i][] = max (dp[i-][], dp[i-][] + a[i]);
                 dp[i][] = max (dp[i-][], dp[i-][] + a[i]);
             }
             else    {
                 int t = s[i-] - '';
                 dp[i][-t] = max (dp[i-][-t], dp[i-][t] + a[i]);
                 dp[i][t] = dp[i-][t];
             }
         }
         else    {
             if (s[i-] == '?')    {
                 int t = s[i] - '';
                 dp[i][t] = max (dp[i-][t], dp[i-][-t] + a[i]);
             }
             else    {
                 int tt = s[i-] - '', t = s[i] - '';
                 dp[i][t] = dp[i-][tt] + ((tt != t) ? a[i] : );
             }
         }
     }

     if (s[n] == '?')    {
         return max (dp[n][], dp[n][]);
     }
     else return dp[n][s[n]-''];
 }

 int main(void)    {        //HDOJ 5375 Gray code
     int T, cas = ;    scanf ("%d", &T);
     while (T--)    {
         scanf ("%s", s + );
         int len = strlen (s + );
         for (int i=; i<=len; ++i)    scanf ("%d", &a[i]);
         printf ("Case #%d: %d\n", ++cas, work (len));
     }

     return ;
 }