func_code_string: #include <bits/stdc++.h>   bool m1;   FILE *Input = stdin, *Output = stdout;   const int maxn = 1e5 + 5;   struct Edge {     int to, next;     Edge(){};     Edge(int ar1, int ar2) {       to = ar1;       next = ar2;     }   } Tree_List[maxn << 1], Tree2_List[maxn << 2];   int Numt[maxn], tott, deg[maxn], totn;   int Numt2[maxn << 1], tott2, size[maxn << 1], Max_Len2;   int Start_Mark, End_Mark, All_Mark[maxn << 1];   int Start, End, All[maxn << 1], Max_Len, next[maxn];   bool Found, onLine[maxn << 1], Mark[maxn << 1];   bool m2;   void Add_Tree(int ar1, int ar2) {     Tree_List[++tott] = Edge(ar2, Numt[ar1]);     Numt[ar1] = tott;   }   void Add_Tree2(int ar1, int ar2) {     Tree2_List[++tott2] = Edge(ar2, Numt2[ar1]);     Numt2[ar1] = tott2;   }   void Get_next(int ar1, int ar2) {     next[ar1] = ar1;     for (int i = Numt[ar1]; i; i = Tree_List[i].next) {       int hh = Tree_List[i].to;       if (hh == ar2) continue;       Get_next(hh, ar1);       if (deg[ar1] == 2) next[ar1] = next[hh];     }   }   void Link(int ar1, int ar2) {     for (int i = Numt[ar1]; i; i = Tree_List[i].next) {       int hh = Tree_List[i].to;       if (hh == ar2 || next[hh] == ar1) continue;       if (deg[next[hh]] == 1 || deg[ar1] == 1) {         Add_Tree2(ar1, next[hh]);         Add_Tree2(next[hh], ar1);         Link(next[hh], ar1);       } else {         Add_Tree2(ar1, hh);         Add_Tree2(hh, ar1);         Link(hh, ar1);       }     }   }   void Get_One_Mark(int ar1, int ar2, int ar3) {     if (Mark[ar1] && ar3 > Max_Len) {       Start_Mark = ar1;       Max_Len = ar3;     }     for (int i = Numt2[ar1]; i; i = Tree2_List[i].next) {       int hh = Tree2_List[i].to;       if (hh == ar2) continue;       Get_One_Mark(hh, ar1, ar3 + 1);     }   }   void Get_the_Other_Mark(int ar1, int ar2, int ar3) {     if (Mark[ar1] && ar3 > Max_Len) {       End_Mark = ar1;       Max_Len = ar3;     }     for (int i = Numt2[ar1]; i; i = Tree2_List[i].next) {       int hh = Tree2_List[i].to;       if (hh == ar2) continue;       Get_the_Other_Mark(hh, ar1, ar3 + 1);     }   }   void Get_One(int ar1, int ar2, int ar3) {     if (ar3 > Max_Len) {       Start = ar1;       Max_Len = ar3;     }     for (int i = Numt2[ar1]; i; i = Tree2_List[i].next) {       int hh = Tree2_List[i].to;       if (hh == ar2) continue;       Get_One(hh, ar1, ar3 + 1);     }   }   void Get_the_Other(int ar1, int ar2, int ar3) {     if (ar3 > Max_Len) {       End = ar1;       Max_Len = ar3;     }     for (int i = Numt2[ar1]; i; i = Tree2_List[i].next) {       int hh = Tree2_List[i].to;       if (hh == ar2) continue;       Get_the_Other(hh, ar1, ar3 + 1);     }   }   void Get_All(int ar1, int ar2, int ar3) {     All[++All[0]] = ar1;     if (ar1 == ar3) {       Found = 1;       return;     }     for (int i = Numt2[ar1]; i; i = Tree2_List[i].next) {       int hh = Tree2_List[i].to;       if (hh == ar2) continue;       Get_All(hh, ar1, ar3);       if (Found) return;     }     All[0]--;   }   void Get_All_Mark(int ar1, int ar2, int ar3) {     if (Mark[ar1]) All[++All[0]] = ar1;     if (ar1 == ar3) {       Found = 1;       return;     }     for (int i = Numt2[ar1]; i; i = Tree2_List[i].next) {       int hh = Tree2_List[i].to;       if (hh == ar2) continue;       Get_All_Mark(hh, ar1, ar3);       if (Found) return;     }     if (Mark[ar1]) All[0]--;   }   void Get_Two(int ar1, int ar2, int ar3) {     if (ar3 > Max_Len) {       Max_Len2 = Max_Len;       End = Start;       Max_Len = ar3;       Start = ar1;     } else if (ar3 > Max_Len2) {       Max_Len2 = ar3;       End = ar1;     }     for (int i = Numt2[ar1]; i; i = Tree2_List[i].next) {       int hh = Tree2_List[i].to;       if (hh == ar2) continue;       Get_Two(hh, ar1, ar3 + 1);     }   }   void Get_size(int ar1, int ar2) {     size[ar1] = 1;     for (int i = Numt2[ar1]; i; i = Tree2_List[i].next) {       int hh = Tree2_List[i].to;       if (hh == ar2) continue;       Get_size(hh, ar1);       size[ar1] += size[hh];     }   }   int main() {     int n;     while (fscanf(Input,  %d , &n) == 1) {       memset(Numt, 0, sizeof(Numt));       memset(Numt2, 0, sizeof(Numt2));       memset(deg, 0, sizeof(deg));       memset(Mark, 0, sizeof(Mark));       memset(onLine, 0, sizeof(onLine));       tott = 0;       totn = n;       tott2 = 0;       for (int i = 1; i < n; i++) {         int h1, h2;         fscanf(Input,  %d %d , &h1, &h2);         Add_Tree(h1, h2);         Add_Tree(h2, h1);         deg[h1]++;         deg[h2]++;       }       int Root = 1;       while (Root <= n && deg[Root] == 2) Root++;       if (Root > n) abort();       Get_next(Root, 0);       Link(Root, 0);       bool Could = 1;       Max_Len = 0;       Get_One(Root, 0, 0);       Max_Len = 0;       Get_the_Other(Start, 0, 0);       Found = All[0] = 0;       Get_All(Start, 0, End);       for (int i = 1; i <= All[0]; i++) onLine[All[i]] = 1;       for (int i = 1; i <= All[0]; i++) {         bool flag = 0;         for (int j = Numt2[All[i]]; j; j = Tree2_List[j].next) {           int hh = Tree2_List[j].to;           if (onLine[hh]) continue;           Get_size(hh, All[i]);           if (size[hh] > 3) {             flag = 1;             break;           }           if (size[hh] == 2) abort();         }         if (flag) {           Could = 0;           break;         }       }       if (Could)         fprintf(Output,  Yes n );       else         fprintf(Output,  No n );     }     fclose(Input);     fclose(Output);     return 0;   }   