Merge pull request #292 from morningsky/master

添加了 面试题02.07.链表相交 0019.删除链表的倒数第N个节点 0206.翻转链表  0206.翻转链表 python3版本

problems/0019.删除链表的倒数第N个节点.md

@@ -112,6 +112,30 @@ class Solution {
     }
 }
 ```
+
+Python:
+```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:
+        head_dummy = ListNode()
+        head_dummy.next = head
+
+        slow, fast = head_dummy, head_dummy
+        while(n!=0): #fast先往前走n步
+            fast = fast.next
+            n -= 1
+        while(fast.next!=None):
+            slow = slow.next
+            fast = fast.next
+        #fast 走到结尾后，slow的下一个节点为倒数第N个节点
+        slow.next = slow.next.next #删除
+        return head_dummy.next
+```
 Go:
 ```Go
 /**

problems/0203.移除链表元素.md

@@ -208,7 +208,23 @@ public ListNode removeElements(ListNode head, int val) {
 ```
 
 Python：
-
+```python
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def removeElements(self, head: ListNode, val: int) -> ListNode:
+        dummy_head = ListNode(next=head) #添加一个虚拟节点
+        cur = dummy_head
+        while(cur.next!=None):
+            if(cur.next.val == val):
+                cur.next = cur.next.next #删除cur.next节点
+            else:
+                cur = cur.next
+        return dummy_head.next
+```
 
 Go：
 

problems/0206.翻转链表.md

@@ -143,7 +143,25 @@ class Solution {
 ```
 
 Python：
-
+```python
+#双指针
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def reverseList(self, head: ListNode) -> ListNode:
+        cur = head   
+        pre = None
+        while(cur!=None):
+            temp = cur.next # 保存一下 cur的下一个节点，因为接下来要改变cur->next
+            cur.next = pre #反转
+            #更新pre、cur指针
+            pre = cur
+            cur = temp
+        return pre
+```
 
 Go：
 

problems/面试题02.07.链表相交.md

@@ -151,7 +151,44 @@ public class Solution {
 ```
 
 Python：
+```python
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
 
+class Solution:
+    def getIntersectionNode(self, headA: ListNode, headB: ListNode) -> ListNode:
+        lengthA,lengthB = 0,0
+        curA,curB = headA,headB
+        while(curA!=None): #求链表A的长度
+            curA = curA.next
+            lengthA +=1
+        
+        while(curB!=None): #求链表B的长度
+            curB = curB.next
+            lengthB +=1
+        
+        curA, curB = headA, headB
+
+        if lengthB>lengthA: #让curA为最长链表的头，lenA为其长度
+            lengthA, lengthB = lengthB, lengthA
+            curA, curB = curB, curA
+
+        gap = lengthA - lengthB #求长度差
+        while(gap!=0): 
+            curA = curA.next #让curA和curB在同一起点上
+            gap -= 1
+        
+        while(curA!=None):
+            if curA == curB:
+                return curA
+            else:
+                curA = curA.next
+                curB = curB.next
+        return None
+```
 
 Go：