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package class10;
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public class Code01_FindFirstIntersectNode {
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public static class Node {
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public int value;
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public Node next;
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public Node(int data) {
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this.value = data;
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}
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}
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public static Node getIntersectNode(Node head1, Node head2) {
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if (head1 == null || head2 == null) {
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return null;
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}
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Node loop1 = getLoopNode(head1);
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Node loop2 = getLoopNode(head2);
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if (loop1 == null && loop2 == null) {
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return noLoop(head1, head2);
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}
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if (loop1 != null && loop2 != null) {
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return bothLoop(head1, loop1, head2, loop2);
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}
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return null;
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}
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// 找到链表第一个入环节点,如果无环,返回null
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public static Node getLoopNode(Node head) {
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if (head == null || head.next == null || head.next.next == null) {
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return null;
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}
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// n1 慢 n2 快
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Node slow = head.next; // n1 -> slow
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Node fast = head.next.next; // n2 -> fast
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while (slow != fast) {
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if (fast.next == null || fast.next.next == null) {
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return null;
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}
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fast = fast.next.next;
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slow = slow.next;
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}
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// slow fast 相遇
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fast = head; // n2 -> walk again from head
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while (slow != fast) {
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slow = slow.next;
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fast = fast.next;
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}
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return slow;
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}
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// 如果两个链表都无环,返回第一个相交节点,如果不想交,返回null
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public static Node noLoop(Node head1, Node head2) {
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if (head1 == null || head2 == null) {
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return null;
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}
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Node cur1 = head1;
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Node cur2 = head2;
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int n = 0;
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while (cur1.next != null) {
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n++;
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cur1 = cur1.next;
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}
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while (cur2.next != null) {
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n--;
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cur2 = cur2.next;
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}
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if (cur1 != cur2) {
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return null;
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}
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// n : 链表1长度减去链表2长度的值
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cur1 = n > 0 ? head1 : head2; // 谁长,谁的头变成cur1
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cur2 = cur1 == head1 ? head2 : head1; // 谁短,谁的头变成cur2
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n = Math.abs(n);
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while (n != 0) {
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n--;
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cur1 = cur1.next;
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}
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while (cur1 != cur2) {
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cur1 = cur1.next;
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cur2 = cur2.next;
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}
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return cur1;
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}
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// 两个有环链表,返回第一个相交节点,如果不想交返回null
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public static Node bothLoop(Node head1, Node loop1, Node head2, Node loop2) {
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Node cur1 = null;
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Node cur2 = null;
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if (loop1 == loop2) {
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cur1 = head1;
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cur2 = head2;
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int n = 0;
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while (cur1 != loop1) {
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n++;
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cur1 = cur1.next;
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}
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while (cur2 != loop2) {
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n--;
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cur2 = cur2.next;
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}
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cur1 = n > 0 ? head1 : head2;
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cur2 = cur1 == head1 ? head2 : head1;
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n = Math.abs(n);
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while (n != 0) {
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n--;
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cur1 = cur1.next;
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}
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while (cur1 != cur2) {
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cur1 = cur1.next;
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cur2 = cur2.next;
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}
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return cur1;
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} else {
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cur1 = loop1.next;
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while (cur1 != loop1) {
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if (cur1 == loop2) {
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return loop1;
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}
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cur1 = cur1.next;
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}
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return null;
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}
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}
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public static void main(String[] args) {
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// 1->2->3->4->5->6->7->null
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Node head1 = new Node(1);
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head1.next = new Node(2);
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head1.next.next = new Node(3);
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head1.next.next.next = new Node(4);
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head1.next.next.next.next = new Node(5);
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head1.next.next.next.next.next = new Node(6);
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head1.next.next.next.next.next.next = new Node(7);
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// 0->9->8->6->7->null
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Node head2 = new Node(0);
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head2.next = new Node(9);
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head2.next.next = new Node(8);
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head2.next.next.next = head1.next.next.next.next.next; // 8->6
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System.out.println(getIntersectNode(head1, head2).value);
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// 1->2->3->4->5->6->7->4...
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head1 = new Node(1);
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head1.next = new Node(2);
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head1.next.next = new Node(3);
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head1.next.next.next = new Node(4);
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head1.next.next.next.next = new Node(5);
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head1.next.next.next.next.next = new Node(6);
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head1.next.next.next.next.next.next = new Node(7);
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head1.next.next.next.next.next.next = head1.next.next.next; // 7->4
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// 0->9->8->2...
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head2 = new Node(0);
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head2.next = new Node(9);
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head2.next.next = new Node(8);
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head2.next.next.next = head1.next; // 8->2
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System.out.println(getIntersectNode(head1, head2).value);
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// 0->9->8->6->4->5->6..
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head2 = new Node(0);
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head2.next = new Node(9);
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head2.next.next = new Node(8);
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head2.next.next.next = head1.next.next.next.next.next; // 8->6
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System.out.println(getIntersectNode(head1, head2).value);
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}
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}
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