POJ 3713 Transferring Sylla （三联通分量）

  1 #include<iostream>
  2 #include<algorithm>
  3 #include<vector>
  4 #include<stack>
  5 #include<queue>
  6 #include<map>
  7 #include<set>
  8 #include<cstdio>
  9 #include<cstring>
 10 #include<cmath>
 11 #include<ctime>
 12 #define fuck(x) cout<<#x<<" = "<<x<<endl;
 13 #define ls (t<<1)
 14 #define rs ((t<<1)+1)
 15 using namespace std;
 16 typedef long long ll;
 17 typedef unsigned long long ull;
 18 const int maxn = 50086;
 19 const int inf = 2.1e9;
 20 const ll Inf = 999999999999999999;
 21 const int mod = 1000000007;
 22 const double eps = 1e-6;
 23 const double pi = acos(-1);
 24 int f[1000];
 25 int index,root,n,m,DEL;
 26 int cnt,Head[1000],v[maxn],Next[maxn];
 27 void init()
 28 {
 29     cnt=0;root=1;
 30     memset(Head,-1,sizeof(Head));
 31     for(int i=0;i<=n;i++){
 32         f[i]=i;
 33     }
 34 }
 35 
 36 inline bool scan_d(int &num)
 37 {
 38         char in;bool IsN=false;
 39         in=getchar();
 40         if(in==EOF) return false;
 41         while(in!=‘-‘&&(in<‘0‘||in>‘9‘)) in=getchar();
 42         if(in==‘-‘){ IsN=true;num=0;}
 43         else num=in-‘0‘;
 44         while(in=getchar(),in>=‘0‘&&in<=‘9‘){
 45                 num*=10,num+=in-‘0‘;
 46         }
 47         if(IsN) num=-num;
 48         return true;
 49 }
 50 void add(int x,int y)
 51 {
 52     cnt++;
 53     v[cnt]=y;
 54     Next[cnt]=Head[x];
 55     Head[x]=cnt;
 56 
 57     cnt++;
 58     v[cnt]=x;
 59     Next[cnt]=Head[y];
 60     Head[y]=cnt;
 61 }
 62 
 63 int num[508],low[508];
 64 bool dfs(int cur,int father)
 65 {
 66     int child=0;
 67     index++;
 68     num[cur]=index;
 69     low[cur]=index;
 70     for(int k=Head[cur];k!=-1;k=Next[k]){
 71         if(v[k]==DEL){continue;}
 72 //        fuck(v[k])
 73         if(num[v[k]]==0){
 74             child++;
 75             if(!dfs(v[k],cur)){return false;}
 76             low[cur]=min(low[cur],low[v[k]]);
 77             if(cur!=root&&low[v[k]]>=num[cur]){
 78                 return false;
 79             }
 80             if(cur==root&&child==2){
 81                 return false;
 82             }
 83         }
 84         else if(v[k]!=father){
 85             low[cur]=min(low[cur],num[v[k]]);
 86         }
 87     }
 88     return true;
 89 }
 90 
 91 bool solve()
 92 {
 93     memset(num,0,sizeof(num));
 94     memset(low,0,sizeof(low));
 95     root=2;
 96     DEL=1;
 97     if(!dfs(2,root)){return false;}
 98     root=1;
 99     for(int i=2;i<=n;i++){
100         memset(num,0,sizeof(num));
101         memset(low,0,sizeof(low));
102         DEL=i;
103         if(!dfs(1,root)){
104 //            cout<<i<<endl;
105             return false;
106         }
107     }
108     return true;
109 }
110 
111 int getf(int x)
112 {
113     if(f[x]==x){return x;}
114     return f[x]=getf(f[x])
115 ;}
116 
117 bool Merge(int x,int y)
118 {
119     int s1=getf(x);
120     int s2=getf(y);
121     if(s1!=s2){
122         f[s1]=s2;
123         return true;
124     }
125     return false;
126 }
127 
128 int main()
129 {
130 //    ios::sync_with_stdio(false);
131 //    freopen("in.txt","r",stdin);
132 
133     while(scanf("%d%d",&n,&m)!=EOF&&n&&m){
134         init();
135         int snum = 0;
136         for(int i=1;i<=m;i++){
137             int x,y;
138             scan_d(x);scan_d(y);
139             add(x+1,y+1);
140             if(Merge(x+1,y+1)){
141                 snum++;
142             }
143         }
144         if(snum!=n-1){printf("NO\n");continue;}
145         memset(num,0,sizeof(num));
146         memset(low,0,sizeof(low));
147         root=1;
148         DEL=0;
149         if(!dfs(1,root)){printf("NO\n");continue;}
150 
151 
152         if(solve()){printf("YES\n");}
153         else printf("NO\n");
154 
155     }
156 
157     return 0;
158 }