1021 Deepest Root (25)

//存到图中，遍历图计算连通块个数，若为1则遍历每个节点当做树根节点，计算层数，存储有最大层数的节点。
//code1:(AC)
#include 
#include 
#include 
#include 
using namespace std;
const int MAXN = 10010;
vector G[MAXN];
bool vis[MAXN], vis2[MAXN];
int N;
void DFS(int v) {
	if(!vis[v]) {
		vis[v] = true;
		for (int i = 0; i < G[v].size(); ++i)
			DFS(G[v][i]);
	}
}
int countDeep(int v) {
	queue q;
	q.push(v);
	vis2[v] = true;  //因为是无向图 
	int layer[MAXN];  ////计层 
	layer[v] = 1; 
	while(!q.empty()) {
		int now = q.front();
		q.pop();
		for (int i = 0; i < G[now].size(); ++i) {
			if(!vis2[G[now][i]]) {
				q.push(G[now][i]);
				vis2[G[now][i]] = true;
				layer[G[now][i]] = layer[now] + 1;	
			}
		}
	}
	int max_layer = -1;
	for(int i=1; i<=N; i++)
		max_layer = max(layer[i], max_layer);
	return max_layer;
}
int main() {	
	scanf("%d",&N);
	for (int i = 0; i < N - 1; ++i) {
		int a, b;
		scanf("%d%d",&a,&b);
		G[a].push_back(b);
		G[b].push_back(a);  //无向图
	}
	int cnt = 0;
	for (int i = 1; i <= N; ++i) {
		if(!vis[i]) {
			DFS(i);
			cnt++;
		}
	}
	if (cnt != 1) {
		printf("Error: %d components",cnt);
		return 0;
	}
	vector collect;
	int MAXD = -1;
	for (int i = 1; i <= N; ++i) {
		memset(vis2,false,sizeof(vis2));
		int D = countDeep(i);
		if(D > MAXD) {
			collect.clear();
			collect.push_back(i);
			MAXD = D;  ////UPDATA 
		} else if(D == MAXD) collect.push_back(i);
	}
	for (int i = 0; i < collect.size(); ++i)
		printf("%d\n",collect[i]);
	return 0;
}
//code2:(卡NO.1测试点)  为啥？？
#include 
#include 
#include 
#include 
using namespace std;
const int MAXN = 10010;
vector G[MAXN];
bool vis[MAXN], vis2[MAXN];
int N;
void DFS(int v) {
	if(!vis[v]) {
		vis[v] = true;
		for (int i = 0; i < G[v].size(); ++i)
			DFS(G[v][i]);
	}
}
int countDeep(int v) {
	queue q;
	q.push(v);
	int D = 1;  ////为啥这样的计层不行？测试没错啊
	vis2[v] = true;  //因为是无向图 
	bool flag2;  ////计层标记 
	while(!q.empty()) {
		int now = q.front();
		q.pop();
		for (int i = 0; i < G[now].size(); ++i) {
			if(!vis2[G[now][i]]) {
				q.push(G[now][i]);
				vis2[G[now][i]] = true;
				flag2 = true;
				//printf("> %d %d\n",D,G[now][i]); 
			}
		}
		if (flag2) D++;
		flag2 = false;
	}
	//printf("\n");
	return D;
}
int main() {	
	scanf("%d",&N);
	for (int i = 0; i < N - 1; ++i) {
		int a, b;
		scanf("%d%d",&a,&b);
		G[a].push_back(b);
		G[b].push_back(a);  //无向图
	}
	int cnt = 0;
	for (int i = 1; i <= N; ++i) {
		if(!vis[i]) {
			DFS(i);
			cnt++;
		}
	}
	if (cnt != 1) {
		printf("Error: %d components",cnt);
		return 0;
	}
	vector collect;
	int MAXD = -1;
	for (int i = 1; i <= N; ++i) {
		memset(vis2,false,sizeof(vis2));
		int D = countDeep(i);
		if(D > MAXD) {
			collect.clear();
			collect.push_back(i);
			MAXD = D;  ////UPDATA 
		} else if(D == MAXD) collect.push_back(i);
	}
	for (int i = 0; i < collect.size(); ++i)
		printf("%d\n",collect[i]);
	return 0;
}