diff --git a/problems/0027.移除元素.md b/problems/0027.移除元素.md
index fd24e8f8..e99fee91 100644
--- a/problems/0027.移除元素.md
+++ b/problems/0027.移除元素.md
@@ -183,28 +183,24 @@ class Solution {
 
 Python：
 
-```python
+```python3
 class Solution:
-    """双指针法
-    时间复杂度：O(n)
-    空间复杂度：O(1)
-    """
-
-    @classmethod
-    def removeElement(cls, nums: List[int], val: int) -> int:
-        fast = slow = 0
-
-        while fast < len(nums):
-
-            if nums[fast] != val:
-                nums[slow] = nums[fast]
-                slow += 1
-
-            # 当 fast 指针遇到要删除的元素时停止赋值
-            # slow 指针停止移动, fast 指针继续前进
-            fast += 1
-
-        return slow
+    def removeElement(self, nums: List[int], val: int) -> int:
+        if nums is None or len(nums)==0: 
+            return 0 
+        l=0
+        r=len(nums)-1
+        while l<r: 
+            while(l<r and nums[l]!=val):
+                l+=1
+            while(l<r and nums[r]==val):
+                r-=1
+            nums[l], nums[r]=nums[r], nums[l]
+        print(nums)
+        if nums[l]==val: 
+            return l 
+        else: 
+            return l+1
 ```
 
 
diff --git a/problems/0028.实现strStr.md b/problems/0028.实现strStr.md
index 1887e91b..271822dc 100644
--- a/problems/0028.实现strStr.md
+++ b/problems/0028.实现strStr.md
@@ -685,7 +685,21 @@ class Solution {
 ```
 
 Python3：
-
+```python
+//暴力解法：
+class Solution(object):
+    def strStr(self, haystack, needle):
+        """
+        :type haystack: str
+        :type needle: str
+        :rtype: int
+        """
+        m,n=len(haystack),len(needle)
+        for i in range(m):
+            if haystack[i:i+n]==needle:
+                return i
+        return -1    
+```	
 ```python
 // 方法一
 class Solution:
diff --git a/problems/0054.螺旋矩阵.md b/problems/0054.螺旋矩阵.md
index 0d79fdf9..8f2691fe 100644
--- a/problems/0054.螺旋矩阵.md
+++ b/problems/0054.螺旋矩阵.md
@@ -171,6 +171,30 @@ class Solution:
 
         return res
 ```
-
+```python3
+class Solution:
+    def spiralOrder(self, matrix: List[List[int]]) -> List[int]:
+        r=len(matrix)
+        if r == 0 or len(matrix[0])==0: 
+            return []
+        c=len(matrix[0])
+        res=matrix[0]
+        
+        if r>1: 
+            for i in range (1,r):
+                res.append(matrix[i][c-1])
+            for j in range(c-2, -1, -1):
+                res.append(matrix[r-1][j])
+            if c>1:    
+                for i in range(r-2, 0, -1):    
+                    res.append(matrix[i][0])
+                    
+        M=[]
+        for k in range(1, r-1):
+            e=matrix[k][1:-1]
+            M.append(e)
+            
+        return res+self.spiralOrder(M) 
+```        
 -----------------------
 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>
diff --git a/problems/0209.长度最小的子数组.md b/problems/0209.长度最小的子数组.md
index c75df661..570242f9 100644
--- a/problems/0209.长度最小的子数组.md
+++ b/problems/0209.长度最小的子数组.md
@@ -179,8 +179,27 @@ class Solution:
                 index += 1
         return 0 if res==float("inf") else res
 ```
-
-
+```python3
+#滑动窗口
+class Solution:
+    def minSubArrayLen(self, target: int, nums: List[int]) -> int:
+        if nums is None or len(nums)==0: 
+            return 0 
+        lenf=len(nums)+1
+        total=0
+        i=j=0
+        while (j<len(nums)):
+            total=total+nums[j]
+            j+=1
+            while (total>=target):
+                lenf=min(lenf,j-i)
+                total=total-nums[i]
+                i+=1
+        if lenf==len(nums)+1:
+            return 0
+        else: 
+            return lenf
+```
 Go：
 ```go
 func minSubArrayLen(target int, nums []int) int {
diff --git a/problems/0234.回文链表.md b/problems/0234.回文链表.md
index eeee6fa5..0dbe88c4 100644
--- a/problems/0234.回文链表.md
+++ b/problems/0234.回文链表.md
@@ -218,59 +218,41 @@ class Solution {
 ```python
 #数组模拟
 class Solution:
-    def isPalindrome(self, head: ListNode) -> bool:
-        length = 0
-        tmp = head
-        while tmp: #求链表长度
-            length += 1
-            tmp = tmp.next
-        
-        result = [0] * length
-        tmp = head
-        index = 0
-        while tmp: #链表元素加入数组
-            result[index] = tmp.val
-            index += 1
-            tmp = tmp.next
-        
-        i, j = 0, length - 1
-        while i < j: # 判断回文
-            if result[i] != result[j]:
+    def isPalindrome(self, head: Optional[ListNode]) -> bool:
+        list=[]
+        while head: 
+            list.append(head.val)
+            head=head.next
+        l,r=0, len(list)-1
+        while l<=r: 
+            if list[l]!=list[r]:
                 return False
-            i += 1
-            j -= 1
-        return True
-        
+            l+=1
+            r-=1
+        return True   
+      
 #反转后半部分链表
 class Solution:
-    def isPalindrome(self, head: ListNode) -> bool:
-        if head == None or head.next == None:
-            return True
-        slow, fast = head, head
-        while fast and fast.next:
-            pre = slow
-            slow = slow.next
-            fast = fast.next.next
-        
-        pre.next = None # 分割链表
-        cur1 = head # 前半部分
-        cur2 = self.reverseList(slow) # 反转后半部分，总链表长度如果是奇数，cur2比cur1多一个节点
-        while cur1:
-            if cur1.val != cur2.val:
-                return False
-            cur1 = cur1.next
-            cur2 = cur2.next
-        return True
+    def isPalindrome(self, head: Optional[ListNode]) -> bool:
+        fast = slow = head
 
-    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
-            cur.next = pre # 反转
-            pre = cur
-            cur = temp
-        return pre
+        # find mid point which including (first) mid point into the first half linked list
+        while fast and fast.next:
+            fast = fast.next.next
+            slow = slow.next
+        node = None
+
+        # reverse second half linked list
+        while slow:
+            slow.next, slow, node = node, slow.next, slow
+
+        # compare reversed and original half; must maintain reversed linked list is shorter than 1st half
+        while node:
+            if node.val != head.val:
+                return False
+            node = node.next
+            head = head.next
+        return True
 ```
 
 ### Go
diff --git a/problems/0704.二分查找.md b/problems/0704.二分查找.md
index 98b55505..eec97a78 100644
--- a/problems/0704.二分查找.md
+++ b/problems/0704.二分查找.md
@@ -220,19 +220,21 @@ class Solution:
 
 （版本二）左闭右开区间
 
-```python
-class Solution:
+```class Solution:
     def search(self, nums: List[int], target: int) -> int:
-        left,right  =0, len(nums)
-        while left < right:
-            mid = (left + right) // 2
-            if nums[mid] < target:
-                left = mid+1
-            elif nums[mid] > target:
-                right = mid
+        if nums is None or len(nums)==0:
+            return -1
+        l=0
+        r=len(nums)-1
+        while (l<=r):
+            m = round(l+(r-l)/2)
+            if nums[m] == target:
+                return m     
+            elif nums[m] > target:
+                r=m-1
             else:
-                return mid
-        return -1
+                l=m+1
+        return -1 
 ```
 
 **Go：**
diff --git a/problems/0925.长按键入.md b/problems/0925.长按键入.md
index 58fe99b7..3924c181 100644
--- a/problems/0925.长按键入.md
+++ b/problems/0925.长按键入.md
@@ -129,29 +129,21 @@ class Solution {
 ```
 ### Python
 ```python
-class Solution:
-    def isLongPressedName(self, name: str, typed: str) -> bool:
-        i, j = 0, 0
-        m, n = len(name) , len(typed)
-        while i< m and j < n:
-            if name[i] == typed[j]: # 相同时向后匹配
-                i += 1
-                j += 1
-            else: # 不相同
-                if j == 0: return False # 如果第一位不相同，直接返回false
-                # 判断边界为n-1,若为n会越界,例如name:"kikcxmvzi" typed:"kiikcxxmmvvzzz"
-                while j < n - 1  and typed[j] == typed[j-1]: j += 1
-                if name[i] == typed[j]:
-                    i += 1
-                    j += 1
-                else: return False
-        # 说明name没有匹配完
-        if i < m: return False
-        # 说明type没有匹配完
-        while j < n:
-            if typed[j] == typed[j-1]: j += 1
-            else: return False
-        return True
+        i = j = 0
+        while(i<len(name) and j<len(typed)):
+        # If the current letter matches, move as far as possible
+            if typed[j]==name[i]:
+                while j+1<len(typed) and typed[j]==typed[j+1]:
+                    j+=1
+                    # special case when there are consecutive repeating letters
+                    if i+1<len(name) and name[i]==name[i+1]:
+                        i+=1
+                else:
+                    j+=1
+                    i+=1
+            else:
+                return False
+        return i == len(name) and j==len(typed)
 ```
 
 ### Go
diff --git a/problems/0977.有序数组的平方.md b/problems/0977.有序数组的平方.md
index a9ee232a..7bc84e85 100644
--- a/problems/0977.有序数组的平方.md
+++ b/problems/0977.有序数组的平方.md
@@ -41,6 +41,15 @@ public:
     }
 };
 ```
+```python3
+class Solution:
+    def sortedSquares(self, nums: List[int]) -> List[int]:
+        res=[]
+        for num in nums: 
+            res.append(num**2)
+        return sorted(res)   
+```	
+        
 
 这个时间复杂度是 O(n + nlogn)， 可以说是O(nlogn)的时间复杂度，但为了和下面双指针法算法时间复杂度有鲜明对比，我记为 O(n + nlog n)。
 
diff --git a/problems/面试题02.07.链表相交.md b/problems/面试题02.07.链表相交.md
index 6ea9a037..abf7a2f8 100644
--- a/problems/面试题02.07.链表相交.md
+++ b/problems/面试题02.07.链表相交.md
@@ -160,6 +160,8 @@ class Solution:
         那么，只要其中一个链表走完了，就去走另一条链表的路。如果有交点，他们最终一定会在同一个
         位置相遇
         """
+        if headA is None or headB is None: 
+            return None
         cur_a, cur_b = headA, headB     # 用两个指针代替a和b