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package com.study.graph;
import java.util.LinkedList;
import java.util.Queue;
/**
* @author ldb
* @date 2019-10-23 15:10
*/
public class Graph {
private int v;
private LinkedList<Integer> adj[]; // 邻接表
public Graph(int v) {
this.v = v;
adj = new LinkedList[v];
for (int i = 0; i < v; ++i) {
adj[i] = new LinkedList<>();
}
}
/**
* 添加边
*
* @param s 顶点
* @param t 顶点
*/
public void addEdge(int s, int t) { // 无向图一条边存两次
adj[s].add(t);
adj[t].add(s);
}
public void bfs(int s, int t) {
if (s == t) return;
// visited是用来记录已经被访问的顶点，用来避免顶点被重复访问。
boolean[] visited = new boolean[v];
visited[s] = true;
// queue是一个队列，用来存储已经被访问、但相连的顶点还没有被访问的顶点。
Queue<Integer> queue = new LinkedList<>();
queue.add(s);
// prev用来记录搜索路径。
int[] prev = new int[v];
for (int i = 0; i < v; ++i) {
prev[i] = -1;
}
while (queue.size() != 0) {
int w = queue.poll();
for (int i = 0; i < adj[w].size(); ++i) {
int q = adj[w].get(i);
if (!visited[q]) {
prev[q] = w;
if (q == t) {
print(prev, s, t);
return;
}
visited[q] = true;
queue.add(q);
}
}
}
}
private void print(int[] prev, int s, int t) { // 递归打印 s->t 的路径
if (prev[t] != -1 && t != s) {
print(prev, s, prev[t]);
}
System.out.print(t + " ");
}
public static void main(String[] args) {
Graph graph = new Graph(8);
graph.addEdge(0,1);
graph.addEdge(0,3);
graph.addEdge(1,2);
graph.addEdge(1,4);
graph.addEdge(2,5);
graph.addEdge(4,5);
graph.addEdge(4,6);
graph.addEdge(5,7);
graph.addEdge(6,7);
// graph.bfs(0,6);
// 深度优先
graph.dfs(0, 6);
}
boolean found = false; // 全局变量或者类成员变量
public void dfs(int s, int t) {
found = false;
boolean[] visited = new boolean[v];
int[] prev = new int[v];
for (int i = 0; i < v; ++i) {
prev[i] = -1;
}
recurDfs(s, t, visited, prev);
print(prev, s, t);
}
private void recurDfs(int w, int t, boolean[] visited, int[] prev) {
if (found == true) return;
visited[w] = true;
if (w == t) {
found = true;
return;
}
for (int i = 0; i < adj[w].size(); ++i) {
int q = adj[w].get(i);
if (!visited[q]) {
prev[q] = w;
recurDfs(q, t, visited, prev);
}
}
}
}