双链表相交问题code

src/ds/linklist/CircleLinkList.java

@@ -1,34 +0,0 @@
-package ds.linklist;
-
-/**
- * 环形链表
- * @author Wen
- * @date 2022/8/31 23:27
- */
-
-public class CircleLinkList {
-
-    /**
-     * 链表是否有环
-     * @return 第一个入环节点
-     */
-    public Node hasCircle(Node head) {
-        if (head == null || head.next == null) {
-            return null;
-        }
-        Node slow = head, quick = head.next;
-        while (slow != quick) {
-            if (slow == null || quick == null) {
-                return null;
-            }
-            slow = slow.next;
-            quick = quick.next.next;
-        }
-        quick = head;
-        while (slow != quick) {
-            slow = slow.next;
-            quick = quick.next;
-        }
-        return slow;
-    }
-}

src/ds/linklist/CircleLinkListQ.java

@@ -14,5 +14,38 @@ package ds.linklist;
  * @date 2022/8/31 23:45
  */
 public class CircleLinkListQ {
+    private final CircleLinkListUtil util = new CircleLinkListUtil();
 
+    public Node findFirstIntersectNode(Node head1, Node head2) {
+        if (head1 == null || head2 == null) {
+            return null;
+        }
+        if (util.hasCircle(head1) == null && util.hasCircle(head2) == null) {
+            return util.bothNoCircle(head1, head2, null);
+        } else if (util.hasCircle(head1) != null && util.hasCircle(head2) != null) {
+            return util.bothCircle(head1, head2);
+        }
+        return null;
+    }
+
+    public static void main(String[] args) {
+        CircleLinkListQ circleLinkListQ = new CircleLinkListQ();
+        Node node1 = new Node(1);
+        Node node2 = new Node(2);
+        Node node3 = new Node(3);
+        Node node4 = new Node(4);
+        Node node5 = new Node(5);
+        Node node6 = new Node(6);
+        Node node7 = new Node(7);
+        Node node8 = new Node(8);
+        Node node9 = new Node(9);
+        node1.next = node2;
+        node2.next = node3;
+        node3.next = node4;
+        node4.next = node5;
+        node5.next = node3;
+        node6.next = node7;
+        node7.next = node5;
+        System.out.println(circleLinkListQ.findFirstIntersectNode(node1, node6).val);
+    }
 }

src/ds/linklist/CircleLinkListUtil.java

@@ -0,0 +1,92 @@
+package ds.linklist;
+
+/**
+ * 环形链表
+ *
+ * @author Wen
+ * @date 2022/8/31 23:27
+ */
+
+public class CircleLinkListUtil {
+
+    /**
+     * 链表是否有环
+     *
+     * @return 第一个入环节点
+     */
+    public Node hasCircle(Node head) {
+        if (head == null || head.next == null || head.next.next == null) {
+            return null;
+        }
+        Node slow = head.next, quick = head.next.next;
+        while (slow != quick) {
+            if (slow == null || quick.next == null) {
+                return null;
+            }
+            slow = slow.next;
+            quick = quick.next.next;
+        }
+        quick = head;
+        while (slow != quick) {
+            slow = slow.next;
+            quick = quick.next;
+        }
+        return slow;
+    }
+
+    public Node bothNoCircle(Node h1, Node h2, Node tail) {
+        if (h1 == null || h2 == null) {
+            return null;
+        }
+        int length1 = 1, length2 = 1;
+        Node n1 = h1, n2 = h2;
+        while (n1.next != tail) {
+            length1++;
+            n1 = n1.next;
+        }
+        while (n2.next != tail) {
+            length2++;
+            n2 = n2.next;
+        }
+        if (n1 == n2) {
+            n1 = length1 <= length2 ? h1 : h2;
+            n2 = n1 == h1 ? h2 : h1;
+        }
+        //长路径先走多出来的步数
+        int i = 0;
+        int remain = Math.abs(length1 - length2);
+        while (i < remain) {
+            n2 = n2.next;
+            i++;
+        }
+        while (n1.next != null && n2.next != null) {
+            if (n1 == n2) {
+                return n1;
+            }
+            n1 = n1.next;
+            n2 = n2.next;
+        }
+        return n1;
+    }
+
+    public Node bothCircle(Node h1, Node h2) {
+        Node c1 = hasCircle(h1);
+        Node c2 = hasCircle(h2);
+        Node l1 = c1.next;
+        while (l1 != c1) {
+            if (l1 == c2) {
+                break;
+            }
+            l1 = l1.next;
+        }
+        //两个不相交的环
+        if (l1 != c2) return null;
+        //两个环相交
+        //1.入环节点为同一节点
+        if (c1 == c2) {
+            return bothNoCircle(h1, h2, l1);
+        } else {
+            return c1;
+        }
+    }
+}