It's strange to find a cut point in poj 1144 ....

It is easy to calculate the number of cut points.

Difficult in some details

It is unclear why dfn is set to 1 at the beginning. Why is it wrong?

IncorrectCode

View code

# Include <stdio. h>
# Include < String . H>
 Int N, son, ans;
 Int Map [ 1000 ] [ 1000 ];
 Int Dfn [ 1000 ], Low [ 1000 ];
 Int Vis [ 1000 ];
 Int Tdfn;
 Int Flag [ 1000 ];
 Int Min ( Int A, Int B ){
 Return A <B? A: B;
}
 Void DFS ( Int U ){
Int V;
 For (V = 1 ; V <= N; V ++ ){
 If (Map [u] [v]) {
 If (! Vis [v]) {
Vis [v] = 1 ;
Tdfn ++;
Low [v] = dfn [v] = tdfn;
DFS (v ); //  To get low [v];  
 Low [u] = min (low [u], low [v]);
If (Low [v]> = dfn [u]) {
 If (U = 1 ) Son ++;
 Else Flag [u] = 1 ;
}
}
 Else Low [u] = min (dfn [v], low [u]);
}
}
}
 Void Init (){
Tdfn = 1 ; Ans =0 ; Vis [ 1 ] = 1 ; Son = 0 ;
Memset (map, 0 , Sizeof (MAP ));
Memset (VIS, 0 , Sizeof (VIS ));
Memset (flag, 0 , Sizeof (FLAG ));
Dfn [ 1 ] = Low [1 ] = 1 ;
}
 Int A [ 1000 ];
 Int Main (){
 Int I = 0 , J;
 Int U, V;
 Char Ch;
 While (Scanf ( "  % D " , & N), n ){
Init ();
 While (Scanf ( "  % D  " , & U), U)
 While (Getchar ()! = '  \ N  ' )
{
Scanf ( "  % D  " , & V );
Map [u] [v] = map [v] [u] = 1 ;
}
DFS ( 1 ); Ans = 0 ;
 If (Son> = 2 ) Ans ++;
 For (I = 1 ; I <= N; I ++) ans + = Flag [I];
Printf ( "  % D \ n  " , ANS );
}
Return   0 ;
}

Real code

View code

# Include <stdio. h>
# Include < String . H>
 Int N, son, ans;
 Int Map [ 110 ] [ 110 ];
 Int Dfn [ 110 ], Low [ 110 ];
 Int Vis [ 110 ];
 Int Tdfn;
 Int Flag [ 110 ];
 Int Min ( Int A, Int B ){
 Return A <B? A: B;
}
 Void DFS ( Int U ){
Int V; dfn [u] = low [u] = ++ tdfn;
 For (V = 1 ; V <= N; V ++ ){
 If (Map [u] [v]) {
 If (! Dfn [v]) {
DFS (v ); //  To get low [v];  
 Low [u] = min (low [u], low [v]);
 If (Low [v]> = dfn [u]) {
 If (U = 1 ) Son ++;
 Else Flag [u] = 1 ;
}
}
 Else Low [u] = min (dfn [v], low [u]);
}
}
}
 Void Init (){
Tdfn = 0 ; Son = 0 ; Ans = 0 ;
Memset (map, 0 ,Sizeof (MAP ));
Memset (flag, 0 , Sizeof (FLAG ));
Memset (dfn, 0 , Sizeof (Dfn ));
}
 Int A [ 110 ];
 Int Main (){
 Int I = 0 , J;
 Int U, V;
 While (Scanf ( "  % D  " , & N), n ){
Init ();
 While (Scanf ( "  % D  " , & U), U)
 While (Getchar ()! = '  \ N  ' )
{
Scanf ( "  % D  " , & V );
Map [u] [v] = map [v] [u] = 1 ;
}
DFS ( 1 );
 If (Son> = 2 ) Ans ++;
 For (I = 2 ; I <= N; I ++) ans + = Flag [I];
Printf ( " % D \ n  " , ANS );
}
 Return   0 ;
}

Name of the adjacent table

# Include <stdio. h> # include <string. h >#include <iostream >#include <vector> using namespace STD; vector <int> list [1000]; int low [1000], DEP [1000]; int Col [1000]; int N, son, ans; int flag [1000]; int min (int A, int B) {return a <B? A: B;} void DFS (INT U, int FA, int t) {Col [u] = 1; Dep [u] = low [u] = T; int Tol = 0; int I, V; for (I = 0; I <list [u]. size (); I ++) {v = list [u] [I]; If (COL [v] = 2) continue; if (COL [v] = 0) {DFS (v, U, t + 1); Tol ++; low [u] = min (low [u], low [v]); If (u = 1 & tol> 1 | low [v]> = Dep [u] & U! = 1) {flag [u] = 1 ;}} else if (COL [v] = 1 & V! = FA) {LOW [u] = min (low [u], DEP [v]) ;}} void Init () {son = 0; ans = 0; memset (flag, 0, sizeof (FLAG); memset (DEP, 0, sizeof (DEP); memset (COL, 0, sizeof (COL ));} int main () {int I = 0, J; int U, V; while (scanf ("% d", & N), n) {Init (); for (I = 0; I <= N; I ++) list [I]. clear (); While (scanf ("% d", & U), u) while (getchar ()! = '\ N') {scanf ("% d", & V); list [u]. push_back (V); list [v]. push_back (U);} DFS (1,-1, 1); for (I = 1; I <= N; I ++) ans + = Flag [I]; printf ("% d \ n", ANS);} return 0 ;}