CF1025D Recovering BST

 1 #include <cstdio>
 2 
 3 const int N = 710;
 4 
 5 int gcd(int ta, int tb) {
 6     if(!tb) {
 7         return ta;
 8     }
 9     return gcd(tb, ta % tb);
10 }
11 
12 inline void read(int &x) {
13     x = 0;
14     char c = getchar();
15     while(c < ‘0‘ || c > ‘9‘) {
16         c = getchar();
17     }
18     while(c >= ‘0‘ && c <= ‘9‘) {
19         x = (x << 3) + (x << 1) + c - 48;
20         c = getchar();
21     }
22     return;
23 }
24 
25 int a[N];
26 bool G[N][N], val[N][N], var[N][N];
27 
28 int main() {
29     int n;
30     read(n);
31     for(int i = 1; i <= n; i++) {
32         read(a[i]);
33     }
34 
35     for(int i = 1; i <= n; i++) {
36         for(int j = i; j <= n; j++) {
37             G[i][j] = G[j][i] = (gcd(a[i], a[j]) > 1);
38         }
39     }
40     for(int i = 1; i <= n; i++) {
41         if(i > 1) {
42             val[i][i] = G[i][i - 1];
43         }
44         if(i < n) {
45             var[i][i] = G[i][i + 1];
46         }
47     }
48 
49     for(int len = 2; len < n; len++) {
50         for(int l = 1; l + len - 1 <= n; l++) {
51             int r = l + len - 1;
52             for(int k = l; k <= r; k++) { // root
53                 bool t = (k == l ? 1 : var[l][k - 1]) & (k == r ? 1 : val[k + 1][r]);
54                 if(!t) {
55                     continue;
56                 }
57                 if(G[k][r + 1]) {
58                     var[l][r] = 1;
59                 }
60                 if(G[k][l - 1]) {
61                     val[l][r] = 1;
62                 }
63             }
64         }
65     }
66 
67     for(int i = 1; i <= n; i++) {
68         bool t = (i == 1 ? 1 : var[1][i - 1]) & (i == n ? 1 : val[i + 1][n]);
69         if(t) {
70             printf("Yes");
71             return 0;
72         }
73     }
74     printf("No");
75     return 0;
76 }