func_code_string: #include <bits/stdc++.h>   using namespace std;   int n, head[100005], tot, de[100005], le[100005], lf[100005];   struct node {     int to, next;   } edge[100005 * 2];   void add_edge(int u, int v) {     de[u]++;     edge[tot].to = v;     edge[tot].next = head[u];     head[u] = tot++;   }   void dfs(int cnt, int pre) {     lf[cnt] = 1;     for (int i = head[cnt]; i != -1; i = edge[i].next) {       int j = edge[i].to;       if (j == pre) continue;       if (de[j] <= 2) dfs(j, cnt);     }   }   int main() {     while (cin >> n) {       tot = 0;       memset(head, -1, sizeof(head));       memset(de, 0, sizeof(de));       memset(lf, 0, sizeof(lf));       memset(le, 0, sizeof(le));       for (int i = 1; i < n; i++) {         int u, v;         cin >> u >> v;         add_edge(u, v);         add_edge(v, u);       }       for (int i = 1; i <= n; i++) {         if (de[i] == 1) dfs(i, 0);       }       for (int i = 1; i <= n; i++) {         for (int j = head[i]; j != -1; j = edge[j].next) {           int k = edge[j].to;           if (lf[k]) le[i]++;         }       }       int flag = 0;       for (int i = 1; i <= n && !flag; i++) {         if (lf[i]) continue;         int cn = 0;         for (int j = head[i]; j != -1; j = edge[j].next) {           int k = edge[j].to;           if (lf[k] == 0 && de[k] - min(2, le[k]) >= 2) cn++;           if (cn > 2) {             flag = 1;             break;           }         }       }       if (flag)         cout <<  NO n ;       else         cout <<  YES n ;     }     return 0;   }   