add leetcode: offer-25-52

Author: CodeWater404

Algorithm/src/offer/_25MergeTwoSortedLists.java

@@ -0,0 +1,36 @@
+package offer;
+
+/**
+ * @author ： CodeWater
+ * @create ：2022-07-04-13:37
+ * @Function Description ：25.合并两个排序的链表
+ */
+public class _25MergeTwoSortedLists {
+    /**
+     * Definition for singly-linked list.
+     * public class ListNode {
+     *     int val;
+     *     ListNode next;
+     *     ListNode(int x) { val = x; }
+     * }
+     */
+    class Solution {
+        public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
+            ListNode virtual = new ListNode(-1) , p = virtual;
+            while( l1 != null && l2 != null ){
+                if( l1.val <= l2.val ) {
+                    p.next = l1;
+                    l1 = l1.next;
+                }else{
+                    p.next = l2;
+                    l2 = l2.next;
+                }
+                p = p.next;
+            }
+
+            p.next = l1 != null ? l1 : l2 ;
+
+            return virtual.next;
+        }
+    }
+}

Algorithm/src/offer/_52TheFirstCommonNodeOfTwoLinkedLists.java

@@ -0,0 +1,32 @@
+package offer;
+
+/**
+ * @author ： CodeWater
+ * @create ：2022-07-04-14:06
+ * @Function Description ：52. 两个链表的第一个公共节点
+ */
+public class _52TheFirstCommonNodeOfTwoLinkedLists {
+    /**
+     * 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) {
+            ListNode p1 = headA , p2 = headB;
+            while( p1 != p2 ){
+                // a链表走完走b，两个交叉走，这样就不用判断边界空的情况
+                p1 = p1 != null ? p1.next : headB;
+                p2 = p2 != null ? p2.next : headA;
+            }
+            // 如果没有相交的点，最终p1和p2都会走到null
+            return p1;
+        }
+    }
+}