Poj 1308 and check the set to determine whether a graph is a tree"

Determine whether a graph is a tree:

Method 1:

Topological sorting:

(1) Exclusive Ring

(2) Except for one node (Root), the inbound traffic of each node is 1.

Method 2:

Query set:

(1) Ensure that the graph is a Unicom graph (non-forest)

(2) to ensure that no rings or similar rings appear (1-> 2, 2-> 3, 1-> 3), merge each edge. If a ring or similar ring appears, the two nodes at the end of the edge will have the same parent node when find_set (the parent node here refers to and queries the collection representatives in the aggregation tree ).

# Include <iostream> <br/> # include <cstring> <br/> using namespace STD; <br/> const int max_size = 100000; <br/> int P [max_size]; <br/> int R [max_size]; <br/> int num = 0; <br/> int ST = 0; <br/> bool flag = false; <br/> void make_set (int x) <br/>{< br/> P [x] = X; <br/> r [x] = 1; <br/>}< br/> int find_set (int x) <br/>{< br/> If (P [x]! = X) <br/> P [x] = find_set (P [x]); <br/> return P [x]; <br/>}< br/> void union_set (int x, int y) <br/>{< br/> If (R [x]> r [y]) <br/> P [y] = x; <br/> else if (R [x] <R [y]) <br/> P [x] = y; <br/> else <br/> {<br/> r [y] ++; <br/> P [x] = y; <br/>}< br/> int main () <br/>{< br/> int U, V; <br/> CIN> U; <br/> CIN> V; <br/> int c = 1; <br/> int I = 0; <br/> while (u! =-1 & V! =-1) <br/>{< br/> If (u = 0 & V = 0) <br/> {<br/> cout <"case" <C <"is a tree. "<Endl; <br/> C ++; <br/> CIN> U; <br/> CIN> V; <br/> continue; <br/>}< br/> ST = 0; <br/> memset (p, 0, sizeof (p); <br/> flag = false; <br/> DO <br/> {<br/> If (P [u] = 0) <br/> {<br/> make_set (U ); <br/> num ++; <br/>}< br/> If (P [v] = 0) <br/>{< br/> make_set (V); <br/> num ++; <br/>}< br/> ST = u; <br/> int T1 = find_set (U); <br/> int t2 = find_set (V ); <Br/> If (T1 = t2) <br/>{< br/> flag = true; <br/>}< br/> union_set (T1, t2); <br/> CIN> U; <br/> CIN> V; <br/>}while (u | V ); <br/> If (flag = true) <br/> cout <"case" <C <"is not a tree. "<Endl; <br/> else if (flag = false) <br/>{< br/> for (I = 0; I <max_size; I ++) <br/>{< br/> If (P [I]! = 0) <br/> If (find_set (I )! = Find_set (ST) <br/>{< br/> cout <"case" <C <"is not a tree. "<Endl; <br/> break; <br/>}< br/> if (I = max_size) <br/> cout <"case" <C <"is a tree. "<Endl; <br/>}< br/> C ++; <br/> CIN> U; <br/> CIN> V; <br/>}< br/>