BZOJ1907 树的路径覆盖

ydc题解上写着贪心，后来又说是树形dp。。。可惜看不懂(顺便骗三连)

其实就是每个叶子开始拉一条链，从下面一路走上来，遇到能把两条链合起来的就合起来就好了。

 /**************************************************************
     Problem: 1907
     User: rausen
     Language: C++
     Result: Accepted
     Time:112 ms
     Memory:1396 kb
 ****************************************************************/

 #include <cstdio>
 #include <cstring>

 using namespace std;
 const int N = 1e4 + ;

 struct edge {
     int next, to;
     edge() {}
     edge(int _n, int _t) : next(_n), to(_t) {}
 } e[N << ];

 struct tree_node {
     int fa, ans, used;
 } tr[N];

 int n;
 int first[N], tot;

 inline int read() {
     int x = ;
     char ch = getchar();
     while (ch < '' || '' < ch)
         ch = getchar();
     while ('' <= ch && ch <= '') {
         x = x *  + ch - '';
         ch = getchar();
     }
     return x;
 }

 void Add_Edges(int x, int y) {
     e[++tot] = edge(first[x], y), first[x] = tot;
     e[++tot] = edge(first[y], x), first[y] = tot;
 }

 #define y e[x].to
 int dfs(int p) {
     int x, cnt = ;
     tr[p].ans = , tr[p].used = ;
     for (x = first[p]; x; x = e[x].next)
         if (y != tr[p].fa) {
             tr[y].fa = p;
             dfs(y);
             tr[p].ans += tr[y].ans;
             if (!tr[y].used) ++cnt;
         }
     if (cnt >= ) tr[p].ans -= , tr[p].used = ;
     else if (cnt == ) --tr[p].ans;
 }
 #undef y

 int main() {
     int i, T;
     T = read();
     while (T--) {
         n = read(), tot = ;
         memset(first, , sizeof(first));
         for (i = ; i < n; ++i)
             Add_Edges(read(), read());
         dfs();
         printf("%d\n", tr[].ans);
     }
     return ;
 }