Added Dequeue in Python

other/nested_brackets.py

@@ -0,0 +1,49 @@
+'''
+The nested brackets problem is a problem that determines if a sequence of
+brackets are properly nested.  A sequence of brackets s is considered properly nested
+if any of the following conditions are true:
+
+	- s is empty
+	- s has the form (U) or [U] or {U} where U is a properly nested string
+	- s has the form VW where V and W are properly nested strings
+
+For example, the string "()()[()]" is properly nested but "[(()]" is not.
+
+The function called is_balanced takes as input a string S which is a sequence of brackets and
+returns true if S is nested and false otherwise.
+
+'''
+
+
+def is_balanced(S):
+
+    stack = []
+    open_brackets = set({'(', '[', '{'})
+    closed_brackets = set({')', ']', '}'})
+    open_to_closed = dict({'{':'}', '[':']', '(':')'})
+
+    for i in range(len(S)):
+
+        if S[i] in open_brackets:
+            stack.append(S[i])
+
+        elif S[i] in closed_brackets:
+            if len(stack) == 0 or (len(stack) > 0 and open_to_closed[stack.pop()] != S[i]):
+                return False
+
+    return len(stack) == 0
+
+
+def main():
+
+    S = input("Enter sequence of brackets: ")
+
+    if is_balanced(S):
+        print(S, "is balanced")
+
+    else:
+        print(S, "is not balanced")
+
+
+if __name__ == "__main__":
+    main()