链表是否是回文结构
package class_03;
import java.util.Stack;
public class Code_11_IsPalindromeList {
public static class Node {
public int value;
public Node next;
public Node(int data) {
this.value = data;
}
}
public static boolean isPalindrome1(Node head) {
Stack<Node> stack = new Stack<Node>();
Node cur = head;
while (cur != null) {
stack.push(cur);
cur = cur.next;
}
while (head != null) {
if (head.value != stack.pop().value) {
return false;
}
head = head.next;
}
return true;
}
public static boolean isPalindrome2(Node head) {
if (head == null || head.next == null) {
return true;
}
Node right = head.next;
Node cur = head;
while (cur.next != null && cur.next.next != null) {
right = right.next;
cur = cur.next.next;
}
Stack<Node> stack = new Stack<Node>();
while (right != null) {
stack.push(right);
right = right.next;
}
while (!stack.isEmpty()) {
if (head.value != stack.pop().value) {
return false;
}
head = head.next;
}
return true;
}
public static boolean isPalindrome3(Node head) {
if (head == null || head.next == null) {
return true;
}
Node n1 = head;
Node n2 = head;
while (n2.next != null && n2.next.next != null) {
n1 = n1.next;
n2 = n2.next.next;
}
n2 = n1.next;
n1.next = null;
Node n3 = null;
while (n2 != null) {
n3 = n2.next;
n2.next = n1;
n1 = n2;
n2 = n3;
}
n3 = n1;
n2 = head;
boolean res = true;
while (n1 != null && n2 != null) {
if (n1.value != n2.value) {
res = false;
break;
}
n1 = n1.next;
n2 = n2.next;
}
n1 = n3.next;
n3.next = null;
while (n1 != null) {
n2 = n1.next;
n1.next = n3;
n3 = n1;
n1 = n2;
}
return res;
}
public static void printLinkedList(Node node) {
System.out.print("Linked List: ");
while (node != null) {
System.out.print(node.value + " ");
node = node.next;
}
System.out.println();
}
public static void main(String[] args) {
Node head = null;
printLinkedList(head);
System.out.print(isPalindrome1(head) + " | ");
System.out.print(isPalindrome2(head) + " | ");
System.out.println(isPalindrome3(head) + " | ");
printLinkedList(head);
System.out.println("=========================");
head = new Node(1);
printLinkedList(head);
System.out.print(isPalindrome1(head) + " | ");
System.out.print(isPalindrome2(head) + " | ");
System.out.println(isPalindrome3(head) + " | ");
printLinkedList(head);
System.out.println("=========================");
head = new Node(1);
head.next = new Node(2);
printLinkedList(head);
System.out.print(isPalindrome1(head) + " | ");
System.out.print(isPalindrome2(head) + " | ");
System.out.println(isPalindrome3(head) + " | ");
printLinkedList(head);
System.out.println("=========================");
head = new Node(1);
head.next = new Node(1);
printLinkedList(head);
System.out.print(isPalindrome1(head) + " | ");
System.out.print(isPalindrome2(head) + " | ");
System.out.println(isPalindrome3(head) + " | ");
printLinkedList(head);
System.out.println("=========================");
head = new Node(1);
head.next = new Node(2);
head.next.next = new Node(3);
printLinkedList(head);
System.out.print(isPalindrome1(head) + " | ");
System.out.print(isPalindrome2(head) + " | ");
System.out.println(isPalindrome3(head) + " | ");
printLinkedList(head);
System.out.println("=========================");
head = new Node(1);
head.next = new Node(2);
head.next.next = new Node(1);
printLinkedList(head);
System.out.print(isPalindrome1(head) + " | ");
System.out.print(isPalindrome2(head) + " | ");
System.out.println(isPalindrome3(head) + " | ");
printLinkedList(head);
System.out.println("=========================");
head = new Node(1);
head.next = new Node(2);
head.next.next = new Node(3);
head.next.next.next = new Node(1);
printLinkedList(head);
System.out.print(isPalindrome1(head) + " | ");
System.out.print(isPalindrome2(head) + " | ");
System.out.println(isPalindrome3(head) + " | ");
printLinkedList(head);
System.out.println("=========================");
head = new Node(1);
head.next = new Node(2);
head.next.next = new Node(2);
head.next.next.next = new Node(1);
printLinkedList(head);
System.out.print(isPalindrome1(head) + " | ");
System.out.print(isPalindrome2(head) + " | ");
System.out.println(isPalindrome3(head) + " | ");
printLinkedList(head);
System.out.println("=========================");
head = new Node(1);
head.next = new Node(2);
head.next.next = new Node(3);
head.next.next.next = new Node(2);
head.next.next.next.next = new Node(1);
printLinkedList(head);
System.out.print(isPalindrome1(head) + " | ");
System.out.print(isPalindrome2(head) + " | ");
System.out.println(isPalindrome3(head) + " | ");
printLinkedList(head);
System.out.println("=========================");
}
}