added 4 new files

nineteen.py

@@ -0,0 +1,10 @@
+input_string = input('enter a string : ')
+frequency = {}
+for i in input_string:
+    if i in frequency:
+        frequency[i] += 1
+    else:
+        frequency[i] = 1
+print(frequency)        
+
+

nineteenone.py

@@ -0,0 +1,11 @@
+input_string = input('enter a string : ')
+string_ = input_string.lower()
+frequency = {}
+for i in string_:
+    if i in frequency:
+        frequency[i] += 1
+    else:
+        frequency[i] = 1
+print(frequency)        
+
+

nineteenthree.py

@@ -0,0 +1,15 @@
+map_={}
+while True:
+    list_=input("enter command : ")
+    cond=list_.split()
+    if cond[0]=='stop':
+            break
+
+    else :
+        if cond[0] in map_  :
+            print ("in if")
+            map_[cond[0]].add(cond[1])
+        else:
+            print("in else")
+            map_[cond[0]]={cond[1]}
+    print(map_)     

nineteentwo.py

@@ -0,0 +1,15 @@
+lst = []
+while True :
+    commands = input()
+    commands = commands.split()
+    if commands[0] == 'stop':
+        break
+    elif commands[0] == 'push':
+        lst.append(commands[1])
+    elif commands[0] == 'pop':
+        index_of_value = lst.index(commands[1])
+        lst.pop(index_of_value)
+    else:
+        print('invalid command')
+
+    print(lst)