Linkedlist를 이용하여 회문 출력

Author: holmir97

PalindromeLinkedLIst/ListNode.java

@@ -0,0 +1,7 @@
+public class ListNode {
+    int val;
+    ListNode next;
+    ListNode() {}
+    ListNode(int val) { this.val = val; }
+    ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+}

PalindromeLinkedLIst/PalindromeLinkedLIst.java

@@ -0,0 +1,84 @@
+import java.util.Stack;
+
+
+// my solution
+public class PalindromeLinkedLIst {
+    public static void main(String[] args) {
+        ListNode list = new ListNode(1, new ListNode(0,new ListNode(1)));
+        System.out.println(new PalindromeLinkedLIst().isPalindrome(list));
+    }
+
+    public boolean isPalindrome(ListNode head) {
+        Stack<Integer> stack = new Stack<>();
+        ListNode head2 = head;
+        int cnt = isCount(head2);
+
+        if (cnt == 1)
+            return true;
+
+        for(int i = 0 ;head != null; i++){
+            if(cnt % 2 == 1 && cnt/2 == i){
+                head = head.next;
+                continue;
+            }
+
+            if (stack.isEmpty()) {
+                stack.push(head.val);
+                head = head.next;
+                continue;
+            }
+            if (stack.peek() != head.val)
+                stack.push(head.val);
+            else
+                stack.pop();
+
+            head = head.next;
+        }
+
+        return stack.isEmpty();
+    }
+
+    public int isCount(ListNode listNode){
+        int cnt =0;
+        while(listNode != null){
+            cnt++;
+            listNode = listNode.next;
+        }
+        return cnt;
+    }
+}
+
+/* best solution_USE REVERSE
+public boolean isPalindrome(ListNode head) {
+    ListNode fast = head, slow = head;
+    while (fast != null && fast.next != null) {
+        fast = fast.next.next;
+        slow = slow.next;
+    }
+    if (fast != null) { // odd nodes: let right half smaller
+        slow = slow.next;
+    }
+    slow = reverse(slow);
+    fast = head;
+
+    while (slow != null) {
+        if (fast.val != slow.val) {
+            return false;
+        }
+        fast = fast.next;
+        slow = slow.next;
+    }
+    return true;
+}
+
+public ListNode reverse(ListNode head) {
+    ListNode prev = null;
+    while (head != null) {
+        ListNode next = head.next;
+        head.next = prev;
+        prev = head;
+        head = next;
+    }
+    return prev;
+}
+ */