【PAT】1021. Deepest Root (25)

1021. Deepest Root (25)

A graph which is connected and acyclic can be considered a tree. The height of the tree depends on the selected root. Now you are supposed to find the root that results in a highest tree. Such a root is called the deepest root.

Input Specification:

Each input file contains one test case. For each case, the first line contains a positive integer N (<=10000) which is the number of nodes, and hence the nodes are numbered from 1 to N. Then N-1 lines follow, each describes an edge by given the two adjacent nodes' numbers.

Output Specification:

For each test case, print each of the deepest roots in a line. If such a root is not unique, print them in increasing order of their numbers. In case that the given graph is not a tree, print "Error: K components" where K is the number of connected components in the graph.

Sample Input 1:

51 21 31 42 5

Sample Output 1:

345

Sample Input 2:

51 31 42 53 4

Sample Output 2:

Error: 2 components

分析：题目要求一个DFS；判断可用并查集或用图；排序习惯用优先队列

细节：主要考察代码熟练度

#include <iostream>#include <cstdio>#include <cmath>#include <queue>#include <vector>#include <functional>using namespace std;const int Max=10001;priority_queue<int, vector<int>, greater<int> > q;class Ver{public:int info;vector<int> link;int num;Ver(){num=0;}Ver(int x){info = x;}}ver[Max];class graph{public:int numver;int numedge;int visited[Max];graph();void insertVer(int x);void insertEdge(int x, int y);int getedge(int v, int x);int DFS(int v, int h);};graph::graph(){numver=numedge=0;for (int i=0;i<Max;++i){visited[i]=0;}}void graph::insertVer(int x){ver[x].info=x;++numver;}void graph::insertEdge(int x, int y){ver[x].link.push_back(y) ;ver[y].link.push_back(x);++ver[x].num;++ver[y].num;++numedge;}int graph::getedge(int v, int x){return ver[v].link[x];}int graph::DFS(int x, int h){visited[x]=1;int tmp=h;for (int i=0;i<ver[x].num;++i){int w=getedge(x,i);if (visited[w]!=1){int t=DFS(w,h+1);if (tmp<t) tmp=t;}}return tmp;}int main(){//freopen("test.txt","r",stdin);graph g;int n;cin>>n;for (int i=1;i<=n;++i){g.insertVer(i);}for (int i=1;i<n;++i){int x,y;cin>>x>>y;g.insertEdge(x,y);}int flag=0;for (int i=1;i<=n;++i){if (g.visited[i]==0){++flag;g.DFS(i,0);}}if (flag!=1) printf("Error: %d components\n",flag);else{int tmp=0;for (int i=1;i<=n;++i){for (int j=1;j<=g.numver;++j) g.visited[j]=0;int t=g.DFS(i,0);if (t>tmp){tmp=t;while (!q.empty()) q.pop();q.push(i);}else if (t==tmp) q.push(i);}while (!q.empty()){printf("%d\n",q.top());q.pop();}}return 0;}