answers for stack practice probs

Author: ellieko

data_structures/5_Stack/stack.py

@@ -6,6 +6,24 @@
 
     reverse_string("We will conquere COVID-19") should return "91-DIVOC ereuqnoc lliw eW"
 '''
+from collections import deque
+
+
+def reverse_string(str):
+    reversed = ""
+    stack = deque()
+    stack.extend(str)
+    l = len(stack)
+    while l != 0:
+        reversed += stack.pop()
+        l -= 1
+    return reversed
+
+
+r1 = reverse_string("hello")
+print(f"reverse string of hello: {r1}")
+r2 = reverse_string("We will conquere COVID-19")
+print(f"reverse string of We will conquere COVID-19: {r2}")
 
 '''
 2. Write a function in python that checks if paranthesis in the string are balanced or not.
@@ -19,3 +37,44 @@
     is_balanced("[a+b]*(x+2y)*{gg+kk}") --> True
     
 '''
+
+
+def is_match(chr):
+    dict = {'}': '{', ']': '[', ')': '('}
+    return dict[chr]
+
+
+def is_balanced(str):
+    stack = deque()
+    for chr in str:
+        if chr in "{([":
+            stack.append(chr)
+        if chr in "})]":
+            if len(stack) == 0 or is_match(chr) != stack.pop():
+                return False
+    return len(stack) == 0
+    """
+    # first solution I wrote has a problem
+    # it doesn't consider when it has equal number of parenthese each side but not the wrong one
+    # {[}] --> gives me True, which is False indeed
+    stack = deque()
+    for chr in str:
+        if chr in "{([":
+            stack.append(chr)
+        if chr in "})]":
+            try:
+                stack.pop()
+            except IndexError:
+                return False
+    return len(stack) == 0
+    """
+
+
+print("is_balanced(\"({a+b}))\"): " + str(is_balanced("({a+b})")))
+print("is_balanced(\"))((a+b}{\"): " + str(is_balanced("))((a+b}{")))
+print("is_balanced(\"((a+b))\"): " + str(is_balanced("((a+b))")))
+print("is_balanced(\"))\"): " + str(is_balanced("))")))
+print("is_balanced(\"[a+b]*(x+2y)*{gg+kk}\") : " +
+      str(is_balanced("[a+b]*(x+2y)*{gg+kk}")))
+
+print("is_balanced(\"({a+b)})\"): " + str(is_balanced("({a+b)}")))