【BZOJ1907】樹的路徑覆蓋【貪心】

【題目鏈接】

清空時候忘把邊清空了= =RE無數發

另外計算的時候還得算根節點...

【ydc的題解】

/* Think Thank Thunk */
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

const int maxn = 10005;

int n, head[maxn], cnt, q[maxn], dp[maxn], pre[maxn];

struct _edge {
	int v, next;
} g[maxn << 1];

inline int iread() {
	int f = 1, x = 0; char ch = getchar();
	for(; ch < '0' || ch > '9'; ch = getchar()) f = ch == '-' ? -1 : 1;
	for(; ch >= '0' && ch <= '9'; ch = getchar()) x = x * 10 + ch - '0';
	return f * x;
}

inline void add(int u, int v) {
	g[cnt] = (_edge){v, head[u]};
	head[u] = cnt++;
}

int main() {
	for(int T = iread(); T; T--) {
		n = iread();
		for(int i = 1; i <= n; i++) head[i] = -1, dp[i] = pre[i] = q[i] = 0; cnt = 0;
		for(int i = 1; i < n; i++) {
			int u = iread(), v = iread();
			add(u, v); add(v, u);
		}

		int h = 0, t = 0;
		pre[q[t++] = 1] = n + 1;
		while(h != t) {
			int u = q[h++];
			for(int i = head[u]; ~i; i = g[i].next) if(!pre[g[i].v]) 
				pre[q[t++] = g[i].v] = u;
		}

		int ans = n;
		for(int i = t - 1; ~i; i--) {
			int u = q[i];
			if(dp[u] == 0) dp[pre[u]]++;
			else if(dp[u] == 1) ans--, dp[pre[u]]++;
			else ans -= 2;
		}

		printf("%d\n", ans);
	}
	return 0;
}