传送门

什么鬼的题？

代码

#include <cstdio>
#include <cstring>
#include <iostream>
#define N 1000001

int n, cnt;
int head[N], to[N << 1], next[N << 1], size[N], cp[N];

inline int read()
{
	int x = 0, f = 1;
	char ch = getchar();
	for(; !isdigit(ch); ch = getchar()) if(ch == ‘-‘) f = -1;
	for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - ‘0‘;
	return x * f;
}

inline void add(int x, int y)
{
	to[cnt] = y;
	next[cnt] = head[x];
	head[x] = cnt++;
}

inline void dfs(int u)
{
	int i, v, rest;
	rest = size[u] = 1;
	for(i = head[u]; i ^ -1; i = next[i])
	{
		v = to[i];
		if(!size[v])
		{
			dfs(v);
			rest += size[v];
			size[u] += size[v];
			cp[u] += cp[v];
			if(cp[v]) rest -= size[v];
		}
	}
	cp[u] += rest >> 1;
}

int main()
{
	int i, x, y;
	n = read();
	memset(head, -1, sizeof(head));
	for(i = 1; i < n; i++)
	{
		x = read();
		y = read();
		add(x, y);
		add(y, x);
	}
	dfs(1);
	printf("%d\n", cp[1]);
	return 0;
}