D. Recovering BST Codeforces Round #505 (rated, Div. 1 + Div. 2, based on VK Cup 2018 Final)

http://codeforces.com/contest/1025/problem/D

树 dp 优化

　　f[x][y][0]=f[x][z][1] & f[z+1][y][0] ( gcd(a[x-1],a[z])<>0 )

　　f[x][y][1]=f[x][z][1] & f[z+1][y][0] ( gcd(a[z],a[y+1])<>0 )

 #include <cstdio>
 #include <cstdlib>
 #include <cmath>
 #include <cstring>
 #include <time.h>
 #include <string>
 #include <set>
 #include <map>
 #include <list>
 #include <stack>
 #include <queue>
 #include <vector>
 #include <bitset>
 #include <ext/rope>
 #include <algorithm>
 #include <iostream>
 using namespace std;
 #define ll long long
 #define minv 1e-6
 #define inf 1e9
 #define pi 3.1415926536
 #define E  2.7182818284
 const ll mod=1e9+;//
 const int maxn=1e3+;

 int a[maxn];
 bool vis[maxn][maxn]={},f[maxn][maxn][]={};

 int main()
 {
     int n,i,j,x,y,z;
     scanf("%d",&n);
     for (i=;i<=n;i++)
         scanf("%d",&a[i]);
     for (i=;i<n;i++)
         for (j=i+;j<=n;j++)
             vis[i][j]=(__gcd(a[i],a[j])!=);
     for (i=;i<=n;i++)
         vis[][i]=,vis[i][n+]=;
     for (i=;i<=n+;i++)
         f[i][i-][]=f[i][i-][]=;
     for (i=;i<=n;i++)
         for (x=,y=i;x<=n-i+;x++,y++)
             for (z=x;z<=y;z++)
                 if (f[x][z-][] && f[z+][y][])
                 {
                     if (vis[x-][z])
                         f[x][y][]=;
                     if (vis[z][y+])
                         f[x][y][]=;
                 }
     if (f[][n][])
         printf("Yes");
     else
         printf("No");
     return ;
 }