regular leetcode

Author: KrisYu

101._symmetric_tree.md

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+###101. Symmetric Tree
+
+题目:
+
+<https://leetcode.com/problems/symmetric-tree/>
+
+
+难度:
+
+Easy
+
+
+两棵树symmetric， 有几种可能：
+
+- 均为none ，symmetric
+- 左孩子，右孩子都不存在，并且值相等， symmetric
+- 右子树 和 另一棵树的左子树相等，左子树 和另一颗树的右子树相等 🌲
+
+
+```
+class Solution(object):
+    def isSymmetric(self, root):
+        """
+        :type root: TreeNode
+        :rtype: bool
+        """
+        if root == None :
+            return True
+        return self.symmetric(root.left, root.right)
+        
+    
+    def symmetric(self,t1, t2):
+        # empty tree
+        if t1 == None or t2 == None:
+            if t1 == t2 == None: 
+                return True
+            else:
+                return False
+        elif t1.val == t2.val:
+            return self.symmetric(t1.left,t2.right) and self.symmetric(t1.right, t2.left)
+        else:
+            return False
+```
+
+其实函数不应该定义为symmetric，应该定义为qual？更合适。
+
+
+

191._number_of_1_bits.md

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+###191. Number of 1 Bits
+
+题目:
+
+<https://leetcode.com/problems/number-of-1-bits/>
+
+
+难度:
+
+Easy
+
+
+转成二进制，数1的个数
+
+```
+class Solution(object):
+    def hammingWeight(self, n):
+        """
+        :type n: int
+        :rtype: int
+        """
+        count = 0
+        while n > 0:
+            count += n % 2
+            n = n//2
+        return count
+```
+
+
+