add java solution for linkedList

Author: Zhanganjin0520

README.md

@@ -198,7 +198,7 @@
 |237|[Node in a Linked List](https://leetcode.com/problems/-node-in-a-linked-list/)| [js](./algorithms/nodeInALinkedList/nodeInALinkedList.js),[java](./algorithms/nodeInALinkedList/Solution.java) |Easy|
 |236|[Lowest Common Ancestor of a Binary Tree](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/)| |Medium|
 |235|[Lowest Common Ancestor of a Binary Search Tree](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/)| |Easy|
-|234|[Palindrome Linked List](https://leetcode.com/problems/palindrome-linked-list/)| |Easy|
+|234|[Palindrome Linked List](https://leetcode.com/problems/palindrome-linked-list/)| [java](./algorithms/palindromeLinkedList/Solution.java) |Easy|
 |233|[Number of Digit One](https://leetcode.com/problems/number-of-digit-one/)| |Medium|
 |232|[Implement Queue using Stacks](https://leetcode.com/problems/implement-queue-using-stacks/)| |Easy|
 |231|[Power of Two](https://leetcode.com/problems/power-of-two/)| |Easy|
@@ -266,7 +266,7 @@
 |163|[Missing Ranges](https://leetcode.com/problems/missing-ranges/) ♥ | |Medium|
 |162|[Find Peak Element](https://leetcode.com/problems/find-peak-element/) | |Medium|
 |161|[One Edit Distance](https://leetcode.com/problems/one-edit-distance/)♥ | |Medium|
-|160|[Intersection of Two Linked Lists](https://leetcode.com/problems/intersection-of-two-linked-lists/) | |Easy|
+|160|[Intersection of Two Linked Lists](https://leetcode.com/problems/intersection-of-two-linked-lists/) | [java](./algorithms/intersectionOfTwoLinkedLists/Solution.java)  |Easy|
 |159|[Longest Substring with At Most Two Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-two-distinct-characters/) ♥ | |Hard|
 |158|[Read N Characters Given Read4 II - Call multiple times](https://leetcode.com/problems/read-n-characters-given-read4-ii-call-multiple-times/) ♥ | |Hard|
 |157|[Read N Characters Given Read4](https://leetcode.com/problems/read-n-characters-given-read4/) ♥ | |Easy|
@@ -285,7 +285,7 @@
 |144|[Binary Tree Preorder Traversal](https://leetcode.com/problems/binary-tree-preorder-traversal/)| [js](./algorithms/binaryTreePreorderTraversal/binaryTreePreorderTraversal.js) |Medium|
 |143|[Reorder List](https://leetcode.com/problems/reorder-list/)| |Medium|
 |142|[Linked List Cycle II](https://leetcode.com/problems/linked-list-cycle-ii/)| |Medium|
-|141|[Linked List Cycle](https://leetcode.com/problems/linked-list-cycle/)| |Medium|
+|141|[Linked List Cycle](https://leetcode.com/problems/linked-list-cycle/)| [java](./algorithms/linkedListCycle/Solution.java) |Medium|
 |140|[Word Break II](https://leetcode.com/problems/word-break-ii/)| |Hard|
 |139|[Word Break](https://leetcode.com/problems/word-break/)| |Medium|
 |138|[Copy List with Random Pointer](https://leetcode.com/problems/copy-list-with-random-pointer/)| |Hard|

algorithms/intersectionOfTwoLinkedLists/Solution.java

@@ -0,0 +1,27 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) {
+ *         val = x;
+ *         next = null;
+ *     }
+ * }
+ */
+public class Solution {
+    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
+        /**
+        定义两个指针, 第一轮让两个到达末尾的节点指向另一个链表的头部, 最后如果相遇则为交点(在第一轮移动中恰好抹除了长度差)
+        两个指针等于移动了相同的距离, 有交点就返回, 无交点就是各走了两条指针的长度
+        **/
+        if(headA == null || headB == null) return null;
+        ListNode pA = headA, pB = headB;
+        // 在这里第一轮体现在pA和pB第一次到达尾部会移向另一链表的表头, 而第二轮体现在如果pA或pB相交就返回交点, 不相交最后就是null==null
+        while(pA != pB) {
+            pA = pA == null ? headB : pA.next;
+            pB = pB == null ? headA : pB.next;
+        }
+        return pA;
+    }
+}

algorithms/linkedListCycle/Solution.java

@@ -0,0 +1,13 @@
+public class Solution {
+    public boolean hasCycle(ListNode head) {
+        // 使用 HashSet 来判断重复
+        Set<ListNode> seen = new HashSet<ListNode>();
+        while (head != null) {
+            if (!seen.add(head)) {
+                return true;
+            }
+            head = head.next;
+        }
+        return false;
+    }
+}

algorithms/palindromeLinkedList/Solution.java

@@ -0,0 +1,32 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public boolean isPalindrome(ListNode head) {
+        List<Integer> vals = new ArrayList<Integer>();
+
+        // 将链表的值复制到数组中
+        ListNode currentNode = head;
+        while (currentNode != null) {
+            vals.add(currentNode.val);
+            currentNode = currentNode.next;
+        }
+
+        // 使用双指针判断是否回文
+        int front = 0;
+        int back = vals.size() - 1;
+        while (front < back) {
+            if (!vals.get(front).equals(vals.get(back))) {
+                return false;
+            }
+            front++;
+            back--;
+        }
+        return true;
+    }
+}