Given a singly linked list, determine if it is a palindrome.
题目含义：给定一个单列表，判断是否构成回文
1 public boolean isPalindrome(ListNode head) { 2 Stack<Integer> valueStack = new Stack<>(); 3 if (head == null) return true; 4 ListNode runer = head; 5 ListNode walker = head; 6 while (runer.next != null && runer.next.next != null) 7 { 8 valueStack.push(walker.val); 9 runer = runer.next.next; 10 walker = walker.next; 11 } 12 if (runer.next != null) 13 { 14 // 列表有偶数个节点 15 if (walker.val != walker.next.val) return false; 16 walker = walker.next.next; 17 }else{ 18 walker = walker.next; 19 } 20 while (walker != null) 21 { 22 if (walker.val != valueStack.pop()) return false; 23 walker = walker.next; 24 } 25 return true; 26 27 }