無向圖

 

 

package com.hisi.test;

import java.util.Deque;
import java.util.LinkedList;

public class Graph {
    private int vertexNum;             // 頂點個數
    private LinkedList<Integer> adjacencyTable[]; // 鄰接表

    public Graph(int vertexNum) {
        this.vertexNum = vertexNum;

        adjacencyTable = new LinkedList[vertexNum];
        for (int i = 0; i < vertexNum; ++i) {
            adjacencyTable[i] = new LinkedList<>();
        }
    }

    public void addEdge(int from, int to) { // 無向圖一條邊存兩次
        adjacencyTable[from].add(to);
        adjacencyTable[to].add(from);
    }

    /**
     * 創建
     *
     * 1  -  2  -  3
     * 丨    丨    丨
     * 4  -  5  -  6
     */
    public void build() {
        addEdge(1, 2);
        addEdge(1, 4);

        addEdge(2, 3);
        addEdge(2, 5);

        addEdge(3, 6);
        addEdge(4, 5);
        addEdge(5, 6);

        for (LinkedList<Integer> list: adjacencyTable) {
            for(Integer i: list) {
                System.out.print(" " + i);
            }
            System.out.println();
        }
    }

    public void printProcess(Integer[] process, Integer index) {
        if (index >= 0) {
            printProcess(process, process[index]);
            System.out.print(index + "    ");
        }
    }



    /**
     * 深度優先搜索 （借助棧）
     */
    public void dfs(int start, int target) {
        if (start == target) {
            return;
        }

        //節點是否訪問過了
        Boolean[] hasEnHeap = new Boolean[vertexNum];
        for (int i = 1; i < vertexNum; i++) {
            hasEnHeap[i] = false;
        }

        //遍歷的輔助隊列
        Deque<Integer> heap = new LinkedList<>();
        heap.offer(start);
        hasEnHeap[start] = true;

        //遍歷的過程(存上一個節點的index)
        Integer[] process = new Integer[vertexNum];
        for(int i=0; i<process.length; i++) {
            process[i] = -1;
        }

        while (!heap.isEmpty()) {
            //棧頂出棧
            Integer top = heap.pollLast();

            //top能到達的點入隊
            for (Integer topCanReceive : adjacencyTable[top]) {
                if (topCanReceive == target) {
                    process[topCanReceive] = top;
                    printProcess(process, topCanReceive);
                    return;
                }
                if (!hasEnHeap[topCanReceive]) {  //節點出棧時，把跟節點連接的所有節點都入棧（已經入過棧的就不入棧了）
                    heap.offerLast(topCanReceive);
                    hasEnHeap[topCanReceive] = true;
                    process[topCanReceive] = top;
                }
            }
        }
    }

    public static void main(String[] args) {
        Graph graph = new Graph(7);  // 比實際頂點數+1
        graph.build();

        

        graph.dfs(1, 6);
    }
}

2 4
1 3 5
2 6
1 5
2 4 6
3 5
1 4 5 6 //打印路徑