判斷一個單鏈表結構的字符串是否是迴文結構
package com.inspire.chapter6;
import java.util.Stack;
public class Code02_IsPalindromeList {
public static class Node {
public int value;
public Node next;
public Node(int v) {
value = v;
}
}
public static boolean isPalindrome1(Node head) {
Stack<Node> stack = new Stack<>();
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 selftest(Node head) {
if (head.next == null) {
return true;
} else if ((head.next.next == null) && (head.value == head.next.value)) {
return true;
}
Node slow = head.next;
Node fast = head.next.next;
while (fast.next != null && fast.next.next != null) {
slow = slow.next;
fast = fast.next.next;
}
Node temp = slow.next;
Stack<Node> stack = new Stack<>();
while (temp != null) {
stack.push(temp);
temp = temp.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 main(String[] args) {
Node head = null;
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);
System.out.println(isPalindrome1(head));
System.out.println(selftest(head));
System.out.println(isPalindrome3(head));
}
}