Given an incomplete bracket sequence S. The task is to find the number of closing brackets ‘)’ needed to make it a regular bracket sequence and print the complete bracket sequence. You are allowed to add the brackets only at the end of the given bracket sequence. If it is not possible to complete the bracket sequence, print “IMPOSSIBLE”.
Let us define a regular bracket sequence in the following way:
- Empty string is a regular bracket sequence.
- If s is a regular bracket sequence, then (s) is a regular bracket sequence.
- If s & t are regular bracket sequences, then st is a regular bracket sequence.
Input : str = “(()(()(”
Output : (()(()()))
Explanation : The minimum number of ) needed to make the sequence regular are 3 which are appended at the end.
Input : str = “())(()”
Output : IMPOSSIBLE
We need to add minimal number of closing brackets ‘)’, so we will count the number of unbalanced opening brackets and then we will add that amount of closing brackets. If at any point the number of the closing bracket is greater than the opening bracket then the answer is IMPOSSIBLE.
Below is the implementation of the above approach:
# Python 3 program to find number of
# closing brackets needed and complete
# a regular bracket sequence
# Function to find number of closing
# brackets and complete a regular
# bracket sequence
# Finding the length of sequence
n = len(s)
open = 0
close = 0
for i in range(n):
# Counting opening brackets
if (s[i] == ‘(‘):
open += 1
# Counting closing brackets
close += 1
# Checking if at any position the
# number of closing bracket
# is more then answer is impossible
if (close > open):
# If possible, print ‘s’ and
# required closing brackets.
print(s, end = “”)
for i in range(open – close):
print(“)”, end = “”)
# Driver code
if __name__ == “__main__”:
s = “(()(()(”
# This code is contributed by ita_c
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