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205 lines
5.2 KiB
205 lines
5.2 KiB
package class09;
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import java.util.Stack;
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public class Code02_IsPalindromeList {
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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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// need n extra space
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public static boolean isPalindrome1(Node head) {
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Stack<Node> stack = new Stack<Node>();
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Node cur = head;
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while (cur != null) {
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stack.push(cur);
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cur = cur.next;
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}
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while (head != null) {
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if (head.value != stack.pop().value) {
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return false;
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}
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head = head.next;
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}
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return true;
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}
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// need n/2 extra space
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public static boolean isPalindrome2(Node head) {
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if (head == null || head.next == null) {
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return true;
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}
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Node right = head.next;
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Node cur = head;
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while (cur.next != null && cur.next.next != null) {
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right = right.next;
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cur = cur.next.next;
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}
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Stack<Node> stack = new Stack<Node>();
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while (right != null) {
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stack.push(right);
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right = right.next;
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}
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while (!stack.isEmpty()) {
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if (head.value != stack.pop().value) {
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return false;
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}
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head = head.next;
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}
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return true;
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}
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// need O(1) extra space
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public static boolean isPalindrome3(Node head) {
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if (head == null || head.next == null) {
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return true;
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}
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Node n1 = head;
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Node n2 = head;
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while (n2.next != null && n2.next.next != null) { // find mid node
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n1 = n1.next; // n1 -> mid
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n2 = n2.next.next; // n2 -> end
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}
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// n1 中点
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n2 = n1.next; // n2 -> right part first node
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n1.next = null; // mid.next -> null
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Node n3 = null;
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while (n2 != null) { // right part convert
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n3 = n2.next; // n3 -> save next node
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n2.next = n1; // next of right node convert
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n1 = n2; // n1 move
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n2 = n3; // n2 move
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}
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n3 = n1; // n3 -> save last node
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n2 = head;// n2 -> left first node
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boolean res = true;
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while (n1 != null && n2 != null) { // check palindrome
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if (n1.value != n2.value) {
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res = false;
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break;
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}
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n1 = n1.next; // left to mid
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n2 = n2.next; // right to mid
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}
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n1 = n3.next;
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n3.next = null;
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while (n1 != null) { // recover list
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n2 = n1.next;
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n1.next = n3;
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n3 = n1;
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n1 = n2;
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}
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return res;
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}
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public static void printLinkedList(Node node) {
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System.out.print("Linked List: ");
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while (node != null) {
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System.out.print(node.value + " ");
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node = node.next;
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}
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System.out.println();
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}
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public static void main(String[] args) {
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Node head = null;
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printLinkedList(head);
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System.out.print(isPalindrome1(head) + " | ");
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System.out.print(isPalindrome2(head) + " | ");
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System.out.println(isPalindrome3(head) + " | ");
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printLinkedList(head);
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System.out.println("=========================");
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head = new Node(1);
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printLinkedList(head);
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System.out.print(isPalindrome1(head) + " | ");
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System.out.print(isPalindrome2(head) + " | ");
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System.out.println(isPalindrome3(head) + " | ");
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printLinkedList(head);
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System.out.println("=========================");
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head = new Node(1);
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head.next = new Node(2);
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printLinkedList(head);
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System.out.print(isPalindrome1(head) + " | ");
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System.out.print(isPalindrome2(head) + " | ");
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System.out.println(isPalindrome3(head) + " | ");
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printLinkedList(head);
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System.out.println("=========================");
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head = new Node(1);
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head.next = new Node(1);
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printLinkedList(head);
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System.out.print(isPalindrome1(head) + " | ");
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System.out.print(isPalindrome2(head) + " | ");
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System.out.println(isPalindrome3(head) + " | ");
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printLinkedList(head);
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System.out.println("=========================");
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head = new Node(1);
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head.next = new Node(2);
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head.next.next = new Node(3);
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printLinkedList(head);
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System.out.print(isPalindrome1(head) + " | ");
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System.out.print(isPalindrome2(head) + " | ");
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System.out.println(isPalindrome3(head) + " | ");
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printLinkedList(head);
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System.out.println("=========================");
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head = new Node(1);
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head.next = new Node(2);
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head.next.next = new Node(1);
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printLinkedList(head);
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System.out.print(isPalindrome1(head) + " | ");
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System.out.print(isPalindrome2(head) + " | ");
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System.out.println(isPalindrome3(head) + " | ");
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printLinkedList(head);
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System.out.println("=========================");
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head = new Node(1);
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head.next = new Node(2);
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head.next.next = new Node(3);
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head.next.next.next = new Node(1);
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printLinkedList(head);
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System.out.print(isPalindrome1(head) + " | ");
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System.out.print(isPalindrome2(head) + " | ");
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System.out.println(isPalindrome3(head) + " | ");
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printLinkedList(head);
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System.out.println("=========================");
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head = new Node(1);
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head.next = new Node(2);
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head.next.next = new Node(2);
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head.next.next.next = new Node(1);
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printLinkedList(head);
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System.out.print(isPalindrome1(head) + " | ");
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System.out.print(isPalindrome2(head) + " | ");
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System.out.println(isPalindrome3(head) + " | ");
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printLinkedList(head);
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System.out.println("=========================");
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head = new Node(1);
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head.next = new Node(2);
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head.next.next = new Node(3);
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head.next.next.next = new Node(2);
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head.next.next.next.next = new Node(1);
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printLinkedList(head);
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System.out.print(isPalindrome1(head) + " | ");
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System.out.print(isPalindrome2(head) + " | ");
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System.out.println(isPalindrome3(head) + " | ");
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printLinkedList(head);
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System.out.println("=========================");
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}
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}
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