链表判环问题
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给定一单链表的头指针head
1、判断链表是否又环。
2、如果有环,求环长以及环的起始节点。
package aglist; class Node{ public final int value; public Node next = null; Node(int value){ this.value = value; } public static void addTail(Node head,Node node){ Node temp = head; while(temp.next != null){ temp = temp.next; } temp.next = node; } public static Node getNode(Node head,int index){ int i = 0; Node temp = head; while(i < index && temp.next != null){ temp = temp.next; i++; } return temp; } public static Node getTail(Node head){ Node temp = head; while(temp.next != null){ temp = temp.next; } return temp; } } public class Circle { public static boolean hasCircle(Node head){ Node fast = head,slow = head;//两指针,一个步长为1,一个步长为2 while(fast.next != null && fast.next.next != null){ slow = slow.next; fast = fast.next.next; if(fast == slow){return true;}//两指针相遇,必有环,且相遇点在环内 } return false; } private static Node getMeetNode(Node head){ Node fast = head,slow = head; while(fast.next != null && fast.next.next != null){ slow = slow.next; fast = fast.next.next; if(fast == slow){break;} } return fast; } private static int getLengthOfCircle(Node meetNode){ int length = 1; Node temp = meetNode.next; while(temp != meetNode){//由于相遇点必在环内,只要顺着环走一圈,即可获得环的长度 length++; temp = temp.next; } return length; } /* * 在相遇点将环分开,视为形成两个单链表 * 一个单链表以head为头 * 另一个单链表以meetNode为头 * 该问题进而规约为求两个单链表的交点,交点即为环的起点 * 并且其交点到两链表头等长 * */ private static Node getStartOfCircle(Node head,Node meetNode){ while(head != meetNode){ head = head.next; meetNode = meetNode.next; } return meetNode; } public static void main(String[] args) { // TODO Auto-generated method stub try { int[] ary = {3,4,5,7,1,40,10,50}; Node head = new Node(30); for (int i = 0; i < ary.length; i++) { Node.addTail(head, new Node(ary[i])); } Node.getTail(head).next = Node.getNode(head, 0); if (hasCircle(head)) { Node meetNode = getMeetNode(head); int lenght = getLengthOfCircle(meetNode); Node start = getStartOfCircle(head, meetNode); System.out.println("length:"+lenght); System.out.println("StartNode:"+start.value); } } catch (Exception e) { // TODO: handle exception e.printStackTrace(); } } }
package aglist;
class Node{public final int value;public Node next = null;Node(int value){this.value = value;}public static void addTail(Node head,Node node){Node temp = head;while(temp.next != null){temp = temp.next;}temp.next = node;}public static Node getNode(Node head,int index){int i = 0;Node temp = head;while(i < index && temp.next != null){temp = temp.next;i++;}return temp;}public static Node getTail(Node head){Node temp = head;while(temp.next != null){temp = temp.next;}return temp;}}public class Circle {public static boolean hasCircle(Node head){Node fast = head,slow = head;//两指针,一个步长为1,一个步长为2while(fast.next != null && fast.next.next != null){slow = slow.next;fast = fast.next.next;if(fast == slow){return true;}//两指针相遇,必有环,且相遇点在环内}return false;}private static Node getMeetNode(Node head){Node fast = head,slow = head;while(fast.next != null && fast.next.next != null){slow = slow.next;fast = fast.next.next;if(fast == slow){break;}}return fast;}private static int getLengthOfCircle(Node meetNode){int length = 1;Node temp = meetNode.next;while(temp != meetNode){//由于相遇点必在环内,只要顺着环走一圈,即可获得环的长度length++;temp = temp.next;}return length;}/* * 在相遇点将环分开,视为形成两个单链表 * 一个单链表以head为头 * 另一个单链表以meetNode为头 * 该问题进而规约为求两个单链表的交点,交点即为环的起点 * 并且其交点到两链表头等长 * */private static Node getStartOfCircle(Node head,Node meetNode){while(head != meetNode){head = head.next;meetNode = meetNode.next;}return meetNode;}public static void main(String[] args) {// TODO Auto-generated method stubtry {int[] ary = {3,4,5,7,1,40,10,50};Node head = new Node(30);for (int i = 0; i < ary.length; i++) {Node.addTail(head, new Node(ary[i]));}Node.getTail(head).next = Node.getNode(head, 0);if (hasCircle(head)) {Node meetNode = getMeetNode(head);int lenght = getLengthOfCircle(meetNode);Node start = getStartOfCircle(head, meetNode);System.out.println("length:"+lenght);System.out.println("StartNode:"+start.value);}} catch (Exception e) {// TODO: handle exceptione.printStackTrace();}}
}
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