CF792C Divide by Three

思路：

dp。

实现：

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <string>
 #include <algorithm>
 using namespace std;

 const int INF = 0x3f3f3f3f;

 string s;
 int n, cnt = ;
 int dp[][][];
 int path[][][];
 int ans[];

 int trans(int index)
 {
     return s[index] - '';
 }

 int dfs(int now, bool lz, int mod)
 {
     if (dp[now][lz][mod] != -)
         return dp[now][lz][mod];
     if (now == n)
     {
         if (lz && !mod)
             return ;
         return -INF;
     }
     int x, y = -INF;
     x = dfs(now + , lz, mod);
     path[now][lz][mod] = ;
     if (s[now] != '' || (s[now] == '' && lz))
     {
         y = dfs(now + , true, (mod + trans(now)) % ) + ;
         if (y > x)
         {
             path[now][lz][mod] = ;
             return dp[now][lz][mod] = y;
         }
     }
     return dp[now][lz][mod] = x;
 }

 void get_path(int now, bool lz, int mod)
 {
     if (now == n)
         return;
     if (path[now][lz][mod])
     {
         ans[cnt++] = now;
         get_path(now + , true, (mod + trans(now)) % );
     }
     else
     {
         get_path(now + , lz, mod);
     }
 }

 int main()
 {
     cin >> s;
     n = s.length();
     memset(dp, -, sizeof(dp));
     int tmp = dfs(, false, );
     if (tmp <= )
     {
         if (s.find("") != string::npos)
             puts("");
         else
             puts("-1");
     }
     else
     {
         get_path(, false, );
         for (int i = ; i < cnt; i++)
         {
             putchar(s[ans[i]]);
         }
         puts("");
     }
     return ;
 }