dfs 2

Author: iScript

.idea/workspace.xml

@@ -0,0 +1,7 @@
+4 6
+0 1
+0 2
+0 3
+1 2
+1 3
+2 3

g2.txt

@@ -0,0 +1,50 @@
+
+//二分图检测
+public class BipartitionDetection {
+    private Graph G;
+    private boolean[] visited;
+    private int[] colors;
+    private boolean isBipartite = true;
+
+    public BipartitionDetection(Graph G){
+        this.G = G;
+        visited = new boolean[G.V()];
+        colors = new int[G.V()];
+
+        for(int i=0;i<G.V();i++) colors[i] = -1;
+
+        // 多包一层for，防止有多个联通分量
+        for(int v = 0 ;v<G.V();v++){
+            if(!visited[v])
+                if(!dfs(v,0)) {
+                    isBipartite = false;break;
+                }
+        }
+    }
+
+    // 深度优先遍历
+    private boolean dfs(int v,int color){
+        visited[v] = true;
+        colors[v] = color;
+        // 遍历相邻节点
+        for(int w : G.adj(v)){
+            if(!visited[w]){
+                if(!dfs(w,1-color)) return false;   // 遍历下一个点，染不同颜色
+            }
+            else if(colors[w] == colors[v]) return false;   // 如果相邻被访问过且相等，则是同一颜色，不是二分图。二分图边的两点隶属于不同的2部分
+        }
+        return true;
+    }
+
+    public boolean isBipartite(){
+        return isBipartite;
+    }
+
+
+    public static void main(String[] args){
+
+        Graph g = new Graph("g2.txt");
+        BipartitionDetection bipartitionDetection = new BipartitionDetection(g);
+        System.out.println(bipartitionDetection.isBipartite());
+    }
+}

out/production/Graph/BipartitionDetection.class

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+import java.util.ArrayList;
+
+public class CycleDetection {
+
+    private Graph G;
+    private boolean[] visited;
+    private boolean hasCycle = false;
+
+    public CycleDetection(Graph G){
+        this.G = G;
+        visited = new boolean[G.V()];
+
+        // 多包一层for，防止有多个联通分量
+        for(int v = 0 ;v<G.V();v++){
+            if(!visited[v])
+                if(dfs(v,v)) {
+                    hasCycle = true;break;
+                }
+
+        }
+    }
+
+    // 从顶点v开始，判断图中是否有环
+    private boolean dfs(int v,int parent){
+        visited[v] = true;
+        // 遍历相邻节点
+        for(int w : G.adj(v)){
+            if(!visited[w])
+                if(dfs(w,v)) return true;           //
+            else if(w != parent)    // 判断是否有环：一个相邻节点w被访问过并且 该相邻节点w不是当前节点v的上个节点，则说明有环
+                return true;
+        }
+        return false;
+    }
+
+    // 是否有环
+    public boolean hasCycle(){
+        return hasCycle;
+    }
+
+
+    public static void main(String[] args){
+
+        Graph g = new Graph("g.txt");
+        CycleDetection cycleDetection = new CycleDetection(g);
+        System.out.println(cycleDetection.hasCycle());
+
+    }
+}

out/production/Graph/CycleDetection.class

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+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+
+//
+public class Path {
+    private Graph G;
+    private int s;
+    private int t;
+    private boolean[] visited;
+    private int[] pre;
+
+
+    public Path(Graph G , int s, int t){
+        G.validateVertex(s);
+        G.validateVertex(s);
+
+        this.G = G;
+        this.s = s; // 原点
+        this.t = t;
+
+        visited = new boolean[G.V()];
+        pre = new int[G.V()];
+
+        for(int i=0;i<pre.length;i++)
+            pre[i] = -1;
+
+        dfs(s,s);
+
+    }
+
+    // 深度优先遍历
+    private boolean dfs(int v,int parent){
+        visited[v] = true;
+        pre[v] = parent;
+
+        if(v == t) return true;
+
+        // 遍历相邻节点
+        for(int w : G.adj(v)){
+            if(!visited[w])
+                if(dfs(w,v) ) return true;
+        }
+
+        return false;
+    }
+
+    // 从源到目标是否可以连接
+    public boolean isConnectedTo(){
+        return visited[t];
+    }
+
+    // 从源到目标的路径
+    public Iterable<Integer> path(){
+        ArrayList<Integer> res = new ArrayList<>();
+        if(!isConnectedTo()) return res;
+
+        int cur = t;
+        while(cur != s){
+            res.add(cur);
+            cur = pre[cur]; // 上一个节点
+        }
+        res.add(s);
+        Collections.reverse(res);   // 反
+        return res;
+    }
+
+
+    public static void main(String[] args){
+
+        Graph g = new Graph("g.txt");
+        Path path = new Path(g,0,6);
+        System.out.println(path.path());
+    }
+}