feat: add python and java solution to leetcode problem: No.0019

Author: yanglbme

basic/sorting/MergeSort/MergeSort.java

@@ -16,9 +16,7 @@ private static void merge(int[] nums, int low, int mid, int high, int[] temp) {
             }
         }
 
-        for (i = low; i <= high; ++i) {
-            nums[i] = temp[i];
-        }
+        System.arraycopy(tmp, low, nums, low, high - low + 1);
     }
 
     private static void mergeSort(int[] nums, int low, int high, int[] temp) {

basic/sorting/MergeSort/README.md

@@ -29,9 +29,7 @@ public class MergeSort {
             }
         }
 
-        for (i = low; i <= high; ++i) {
-            nums[i] = temp[i];
-        }
+        System.arraycopy(tmp, low, nums, low, high - low + 1);
     }
 
     private static void mergeSort(int[] nums, int low, int high, int[] temp) {

solution/0000-0099/0019.Remove Nth Node From End of List/README.md

@@ -33,15 +33,54 @@
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```python
-
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
+        dummy = ListNode(0, head)
+        p = q = dummy
+        for i in range(n):
+            p = p.next
+        while p.next is not None:
+            p = p.next
+            q = q.next
+        q.next = q.next.next
+        return dummy.next
 ```
 
 ### **Java**
 
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```java
-
+/**
+ * Definition for singly-linked list.
+ * 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; }
+ * }
+ */
+class Solution {
+    public ListNode removeNthFromEnd(ListNode head, int n) {
+        ListNode dummy = new ListNode(0, head);
+        ListNode p = dummy, q = dummy;
+        while (n-- > 0) {
+            p = p.next;
+        }
+        while (p.next != null) {
+            p = p.next;
+            q = q.next;
+        }
+        q.next = q.next.next;
+        return dummy.next;
+    }
+}
 ```
 
 ### **...**

solution/0000-0099/0019.Remove Nth Node From End of List/README_EN.md

@@ -33,13 +33,52 @@ After removing the second node from the end, the linked list becomes <strong>1-&
 ### **Python3**
 
 ```python
-
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
+        dummy = ListNode(0, head)
+        p = q = dummy
+        for i in range(n):
+            p = p.next
+        while p.next is not None:
+            p = p.next
+            q = q.next
+        q.next = q.next.next
+        return dummy.next
 ```
 
 ### **Java**
 
 ```java
-
+/**
+ * Definition for singly-linked list.
+ * 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; }
+ * }
+ */
+class Solution {
+    public ListNode removeNthFromEnd(ListNode head, int n) {
+        ListNode dummy = new ListNode(0, head);
+        ListNode p = dummy, q = dummy;
+        while (n-- > 0) {
+            p = p.next;
+        }
+        while (p.next != null) {
+            p = p.next;
+            q = q.next;
+        }
+        q.next = q.next.next;
+        return dummy.next;
+    }
+}
 ```
 
 ### **...**

solution/0000-0099/0019.Remove Nth Node From End of List/Solution.java

@@ -1,20 +1,25 @@
+/**
+ * Definition for singly-linked list.
+ * 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; }
+ * }
+ */
 class Solution {
     public ListNode removeNthFromEnd(ListNode head, int n) {
-        ListNode pre = new ListNode(-1);
-        pre.next = head;
-        ListNode fast = pre;
-        ListNode slow = pre;
-        
-        // 快指针先走 n 步
-        for (int i = 0; i < n; ++i) {
-            fast = fast.next;
+        ListNode dummy = new ListNode(0, head);
+        ListNode p = dummy, q = dummy;
+        while (n-- > 0) {
+            p = p.next;
         }
-        while (fast.next != null) {
-            fast = fast.next;
-            slow = slow.next;
+        while (p.next != null) {
+            p = p.next;
+            q = q.next;
         }
-
-        slow.next = slow.next.next;
-        return pre.next;
+        q.next = q.next.next;
+        return dummy.next;
     }
 }

solution/0000-0099/0019.Remove Nth Node From End of List/Solution.py

@@ -1,25 +1,16 @@
 # Definition for singly-linked list.
 # class ListNode:
-#     def __init__(self, x):
-#         self.val = x
-#         self.next = None
-
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
 class Solution:
-    def removeNthFromEnd(self, head, n):
-        """
-        :type head: ListNode
-        :type n: int
-        :rtype: ListNode
-        """
-        pre=ListNode(-1)
-        pre.next=head
-        fast=pre
-        slow=pre
-        
-        for _ in range(n):
-            fast=fast.next
-        while fast.next:
-            fast=fast.next
-            slow=slow.next
-        slow.next=slow.next.next
-        return pre.next
+    def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
+        dummy = ListNode(0, head)
+        p = q = dummy
+        for i in range(n):
+            p = p.next
+        while p.next is not None:
+            p = p.next
+            q = q.next
+        q.next = q.next.next
+        return dummy.next