poj1182 Food Chain (and find good questions)

And check the classic questions

For each animal create 3 elements, x, x+N, x+2*N (representing that x belongs to class A, class B and class C, respectively).

Putting two elements in a group means they happen at the same time.

Got stuck with illegal data a few times.

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<queue>
 4 #include<cstring>
 5 #include<algorithm>
 6 #include<cmath>
 7 #include<stack>
 8 #define lson l, m, rt<<1
 9 #define rson m+1, r, rt<<1|1
10 #define IO ios::sync_with_stdio(false);cin.tie(0);
11 #define INF 0x3f3f3f3f
12 typedef unsigned long long ll;
13 using namespace std;
14 const int N = 50000;
15 int n, k, d, x, y, ans=0;
16 int pre[50010*3];
17 int find(int x)
18 {
19     while(x != pre[x]){
20         x = pre[x];
21     }
22     return x;
23 }
24 int is_same(int a, int b)
25 {
26     int tx = find(a);
27     pre[a] = tx;
28     int ty = find(b);
29     pre[b] = ty; 
30     if(tx == ty) return 1;
31     else return 0;
32 }
33 void join(int a, int b)
34 {
35     int tx = find(a);
36     int ty = find(b);
37     pre[tx] = ty;
38 }
39 void solve()
40 {
41      if (d == 1 ){ // x and y are equivalent 
42          if (x > n||x<= 0 ||y > n||y<= 0 ){ // invalid 
43              ans++ ;
 44              return ;
 45          }
 46          else  if (is_same(x, y+N)||is_same(x, y+ 2 *N)) // conflict situation, B eats A, C eats A 
47              ans++ ; 
 48          else { 
 49              join(x, y);
 50              join(x+N, y+ N);
 51              join(x+2 *N, y+ 2 * N);
 52          }
 53      }
 54      else  if (d == 2 ){ // x eats y 
55          if (x > n||x<= 0 ||y > n||y< = 0 ){ // Illegal 
56              ans++ ;
 57              return ;
 58          }
 59          else  if (is_same(x, y)||is_same(x, y+ 2 *N)) // conflict situation, A and B, C eats A 
60              ans++ ; 
 61          else { 
62             join(x, y+N);
63             join(x+N, y+2*N);
64             join(x+2*N, y); 
65         }
66     }
67 }
68 int main()
69 {
70     for(int i = 0; i <= N*3; i++){
71         pre[i] = i;
72     }
73     scanf("%d%d", &n, &k);
74     for(int i = 0; i < k; i++){
75         scanf("%d%d%d", &d, &x, &y);
76         solve();
77     }
78     printf("%d\n", ans);
79     return 0;
80 }

poj1182 Food Chain (and find good questions)

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