【ZJOI2017 Round1练习】D8T2 sequence（DP）

题意：

思路：

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

 const int N = , INF = -0x3f3f3f3f;
 int n, m, ans[N], v[N], a[N], last[N][N], f[N][N][N], g[N][N][N];
 map<int, int> hash;

 inline void upt(int &x, const int &y) {
     if (x < y) x = y;
 }

 char ch;
 inline int read() {
     int res = , sgn = ;
     while (ch = getchar(), ch < '' || ch > '') if (ch == '-') break;
     ch == '-' ? sgn =  : res = ch - ;
     while (ch = getchar(), ch >= '' && ch <= '') res = res *  + ch - ;
     return sgn ==  ? res : -res;
 }

 int main() {
   freopen("sequence.in", "r", stdin);
   freopen("sequence.out", "w", stdout);

     n = read();
     for (int i = ; i <= n; ++i) v[i] = read();
     for (int i = ; i <= n; ++i) {
         a[i] = read();
         if (hash[a[i]] == ) hash[a[i]] = ++m;
     }
     for (int i = ; i <= n; ++i) {
         for (int j = ; j <= m; ++j) last[i][j] = last[i - ][j];
         last[i][hash[a[i]]] = i;
     }
     memset(f, INF, sizeof(f));
     memset(g, INF, sizeof(g));
     for (int i = ; i <= n; ++i) {
         for (int j = ; j <= n; ++j)
             if (i + j <= n)
                 f[i][i][j] = g[i][i][j] = v[j + ];
             else     break;
         f[i][i - ][] = g[i][i - ][] = ;
     }
     for (int l = ; l <= n; ++l)
         for (int i = ; i <= n; ++i) {
             int j = i + l;
             if (j > n) break;
             for (int k = ; k <= n; ++k) {
                 if (j + k > n) break;
                 upt(f[i][j][k], f[i][j - ][] + v[k + ]);
                 upt(g[i][j][k], f[i][j - ][] + v[k + ]);
                 int p = hash[a[j] + ], q = hash[a[j] - ];
                 for (int h = last[j][p]; h >= i; h = last[h - ][p])
                     upt(f[i][j][k], f[i][h][k + ] + f[h + ][j - ][]);
                 for (int h = last[j][q]; h >= i; h = last[h - ][q]) {
                     upt(f[i][j][k], g[i][h][k + ] + f[h + ][j - ][]);
                     upt(g[i][j][k], g[i][h][k + ] + f[h + ][j - ][]);
                 }
             }
         }
     ans[] = ;
     for (int i = ; i <= n; ++i) {
         upt(ans[i], ans[i - ]);
         for (int j = ; j < i; ++j)
             upt(ans[i], ans[j] + f[j + ][i][]);
     }
     printf("%d\n", ans[n]);
     return ;
 }