图的遍历 | 1021图的连通块判断 以及 最深的最小生成树

bfs（23分，case3无法通过。经查是bfs结构写错）：

#include <stdio.h>
#include <memory.h>
#include <math.h>
#include <string>
#include <vector>
#include <set>
#include <stack>
#include <queue>
#include <algorithm>
#include <map>


#define I scanf
#define OL puts
#define O printf
#define F(a,b,c) for(a=b;a<c;a++)
#define FF(a,b) for(a=0;a<b;a++)
#define FG(a,b) for(a=b-1;a>=0;a--)
#define LEN 10010
#define MAX 0x06FFFFFF
#define V vector<int>

using namespace std;

int n; 
vector<int> g[LEN];
int vis[LEN];
int deep=0;
set<int> ans;
int block=0;

int main(){
//    freopen("D:\CbWorkspace\PAT\图的遍历

1021_1.txt","r",stdin);
    int a,b,i,j,k;
    I("%d",&n);
    FF(i,n-1){
        I("%d%d",&a,&b);
        g[a].push_back(b);
        g[b].push_back(a);
    }
    for(i=1;i<=n;i++) if(!vis[i]){
        queue<int> q;
        q.push(i);
        int d=0;
        int cnt=1;
        while(!q.empty()){
            d++;
            int s=q.size();
            FF(j,s){
                int t=q.front();
                q.pop();
//                if(vis[t]) continue;
                FF(k,g[t].size()){
                    int tmp=g[t][k];
                    if(vis[tmp]) continue;
                    cnt++;
                    q.push(tmp);
                    vis[tmp]=1;
                }
            }
        }
        if(cnt>=n){
            if(d>deep){
                ans.clear();
                deep=d;
                ans.insert(i);
            }else if(d==deep){
                ans.insert(i);
            }
            memset(vis,0,sizeof vis);
        }else{
            block++;
        }
    }
    if(block>1){
        printf("Error: %d components
",block);
    }else{
        set<int>::iterator it=ans.begin();
        while(it!=ans.end()){
            printf("%d
",*it);
            it++; 
        } 
    }
    return 0;
}

AC代码：

#include <stdio.h>
#include <memory.h>
#include <math.h>
#include <string>
#include <vector>
#include <set>
#include <stack>
#include <queue>
#include <algorithm>
#include <map>


#define I scanf
#define OL puts
#define O printf
#define F(a,b,c) for(a=b;a<c;a++)
#define FF(a,b) for(a=0;a<b;a++)
#define FG(a,b) for(a=b-1;a>=0;a--)
#define LEN 10010
#define MAX 0x06FFFFFF
#define V vector<int>

using namespace std;

int n; 
vector<int> g[LEN];
int vis[LEN];
int deep=0;
set<int> ans;
int block=0;

int main(){
//    freopen("D:\CbWorkspace\PAT\图的遍历\1021_2.txt","r",stdin);
    int a,b,i,j,k;
    I("%d",&n);
    FF(i,n-1){
        I("%d%d",&a,&b);
        g[a].push_back(b);
        g[b].push_back(a);
    }
    for(i=1;i<=n;i++) if(!vis[i]){
        queue<int> q;
        q.push(i);
        int d=0;
        int cnt=1;
        while(!q.empty()){
            d++;
            int sz=q.size();
            while(sz-->0){
                int t=q.front();
                q.pop();
                vis[t]=1;
                FF(k,g[t].size()){
                    int tmp=g[t][k];
                    if(vis[tmp]==0){
                        cnt++;
                        q.push(tmp);
                        vis[tmp]=1;
                    } 
                }
            }
        }
        if(cnt>=n){
            if(d>deep){
                ans.clear();
                deep=d;
                ans.insert(i);
            }else if(d==deep){
                ans.insert(i);
            }
            memset(vis,0,sizeof vis);
        }else{
            block++;
        }
    }
    if(block>1){
        printf("Error: %d components
",block);
    }else{
        set<int>::iterator it=ans.begin();
        while(it!=ans.end()){
            printf("%d
",*it);
            it++; 
        } 
    }
    return 0;
}

注意正确的BFS结构：

queue<int> q;        //建立队列 
q.push(i);            //入队 
while(!q.empty()){    //非空判断 
    int sz=q.size();
    while(sz-->0){    //当前层 
        int t=q.front();    //出队 
        q.pop();
        vis[t]=1;            //出队已访问 
        FF(k,g[t].size()){    //出队顶点的所有后继 
            int tmp=g[t][k];
            if(vis[tmp]==0){    //这个后继未访问 
                q.push(tmp);    //入队 
                vis[tmp]=1;        //入队已访问 
            } 
        }
    }
}

并查集+dfs: