update 198-200

Author: kenwoodjw

README.md

@@ -459,45 +459,53 @@ def singleton(cls):
             instances[cls] = cls(*args, **kwargs)
         return instances[cls]
     return wrapper
+    
+    
 @singleton
 class Foo(object):
     pass
 foo1 = Foo()
 foo2 = Foo()
-print foo1 is foo2 #True
+print(foo1 is foo2)  # True
 ```
 第二种方法：使用基类
 New 是真正创建实例对象的方法，所以重写基类的new 方法，以此保证创建对象的时候只生成一个实例
 ```python
 class Singleton(object):
-    def __new__(cls,*args,**kwargs):
-        if not hasattr(cls,'_instance'):
-            cls._instance = super(Singleton,cls).__new__(cls,*args,**kwargs)
+    def __new__(cls, *args, **kwargs):
+        if not hasattr(cls, '_instance'):
+            cls._instance = super(Singleton, cls).__new__(cls, *args, **kwargs)
         return cls._instance
 
+    
 class Foo(Singleton):
     pass
 
 foo1 = Foo()
 foo2 = Foo()
 
-print foo1 is foo2 #True
+print(foo1 is foo2)  # True
 ```
 第三种方法：元类，元类是用于创建类对象的类，类对象创建实例对象时一定要调用call方法，因此在调用call时候保证始终只创建一个实例即可，type是python的元类
 ```python
 class Singleton(type):
-    def __call__(cls,*args,**kwargs):
-        if not hasattr(cls,'_instance'):
-            cls._instance = super(Singleton,cls).__call__(*args,**kwargs)
+    def __call__(cls, *args, **kwargs):
+        if not hasattr(cls, '_instance'):
+            cls._instance = super(Singleton, cls).__call__(*args, **kwargs)
         return cls._instance
-```
-```python
+
+
+# Python2
 class Foo(object):
     __metaclass__ = Singleton
 
+# Python3
+class Foo(metaclass=Singleton):
+    pass
+
 foo1 = Foo()
 foo2 = Foo()
-print foo1 is foo2 #True
+print(foo1 is foo2)  # True
 
 ```
 ### 18.反转一个整数，例如-123 --> -321 
@@ -867,8 +875,13 @@ def loop_merge_sort(l1,l2):
         else:
             tmp.append(l2[0])
             del l2[0]
-            
-        
+    while len(l1)>0:
+        tmp.append(l1[0])
+        del l1[0]
+    while len(l2)>0:
+        tmp.append(l2[0])
+        del l2[0]
+    return tmp
 ```
 ### 37.给定一个任意长度数组，实现一个函数
 让所有奇数都在偶数前面，而且奇数升序排列，偶数降序排序，如字符串'1982376455',变成'1355798642'