hihoCoder 1062 最近公共祖先·一 最详细的解题报告

  1 import java.util.HashMap;
  2 import java.util.Scanner;
  3 
  4 public class Main {
  5 
  6     private HashMap<String,Integer>nodeMap;
  7     private Node[]nodes;
  8     private int index;
  9     private int ancestorIndex;
 10     
 11     public Main(){
 12         this.nodeMap=new HashMap<String,Integer>();
 13         this.nodes=new Node[1001];
 14         this.index=0;
 15         this.ancestorIndex=-1;
 16     }
 17     
 18     private void reset(){
 19         for(int i=0;i<this.index;i++){
 20             this.nodes[i].isVisited=false;
 21         }
 22         this.ancestorIndex=-1;
 23     }
 24     
 25     private int getNode(String nodeName){        
 26         if(!this.nodeMap.containsKey(nodeName)){
 27             this.nodes[this.index]=new Node(nodeName);
 28             this.nodeMap.put(nodeName, this.index);
 29             this.index++;
 30         }
 31         return this.nodeMap.get(nodeName);
 32     }
 33     
 34     private void visit(int nodeIndex){
 35         if(nodeIndex>=0&&nodeIndex<this.index){
 36             if(this.nodes[nodeIndex].isVisited){
 37                 this.ancestorIndex= nodeIndex;
 38                 return;
 39             }else{
 40                 this.nodes[nodeIndex].isVisited=true;
 41                 int parentIndex=this.nodes[nodeIndex].parentIndex;
 42                 this.visit(parentIndex);
 43             }            
 44         }
 45     }
 46     
 47     public void addNode(String parent,String child){
 48         int parentIndex=this.getNode(parent);
 49         int childIndex=this.getNode(child);
 50         if(parentIndex>=0&&parentIndex<this.index
 51                 &&childIndex>=0&&childIndex<this.index){
 52             this.nodes[childIndex].parentIndex=parentIndex;
 53         }
 54     }
 55     
 56     public void getAncestor(String first,String second){
 57         int firstIndex=this.getNode(first);
 58         int secondIndex=this.getNode(second);
 59         this.visit(firstIndex);
 60         this.visit(secondIndex);
 61         if(this.ancestorIndex>=0&&this.ancestorIndex<this.index){
 62             this.nodes[this.ancestorIndex].print();
 63         }else{
 64             System.out.println("-1");
 65         }
 66         this.reset();
 67     }
 68     
 69     public static void main(String[] args) {
 70         
 71         Scanner scanner=new Scanner(System.in);
 72         Main ancestor=new Main();
 73         int n=scanner.nextInt();
 74         for(int i=0;i<n;i++){
 75             String first=scanner.next();
 76             String second=scanner.next();
 77             ancestor.addNode(first, second);
 78         }
 79         int m=scanner.nextInt();
 80         for(int i=0;i<m;i++){
 81             String first=scanner.next();
 82             String second=scanner.next();
 83             ancestor.getAncestor(first, second);
 84         }
 85     }
 86 
 87 }
 88 
 89 class Node{
 90     public String name;
 91     public int parentIndex;
 92     public boolean isVisited;
 93     public Node(String name){
 94         this.name=name;
 95         this.parentIndex=-1;
 96         this.isVisited=false;
 97     }
 98     public void print(){
 99         System.out.println(this.name);
100     }
101 }