Balanced Brackets - Hackerrank Problem Solution

Balanced Brackets

Hackerrank Problem Solution

PROBLEM STATEMENT

A bracket is considered to be any one of the following characters: (, ), {, }, [, or ].

Two brackets are considered to be a matched pair if the an opening bracket (i.e., (, [, or {) occurs to the left of a closing bracket (i.e., ), ], or }) of the exact same type. There are three types of matched pairs of brackets: [], {}, and ().

A matching pair of brackets is not balanced if the set of brackets it encloses are not matched. For example, {[(])} is not balanced because the contents in between { and } are not balanced. The pair of square brackets encloses a single, unbalanced opening bracket, (, and the pair of parentheses encloses a single, unbalanced closing square bracket, ].

By this logic, we say a sequence of brackets is balanced if the following conditions are met:

• It contains no unmatched brackets.
• The subset of brackets enclosed within the confines of a matched pair of brackets is also a matched pair of brackets.

Given  strings of brackets, determine whether each sequence of brackets is balanced. If a string is balanced, return YES. Otherwise, return NO.

Function Description

Complete the function isBalanced in the editor below. It must return a string: YES if the sequence is balanced or NO if it is not.

isBalanced has the following parameter(s):

• s: a string of brackets

Input Format

The first line contains a single integer , the number of strings.
Each of the next  lines contains a single string , a sequence of brackets.

Constraints

• , where  is the length of the sequence.
• All chracters in the sequences ∈ { {, }, (, ), [, ] }.

Output Format

For each string, return YES or NO.

Sample Input

3
{[()]}
{[(])}
{{[[(())]]}}

Sample Output

YES
NO
YES

Explanation

1. The string {[()]} meets both criteria for being a balanced string, so we print YES on a new line.
2. The string {[(])} is not balanced because the brackets enclosed by the matched pair { and } are not balanced: [(]).
3. The string {{[[(())]]}} meets both criteria for being a balanced string, so we print YES on a new line.

 .

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SOLUTION

def is_matched(expression): stack = [] for i in expression: if (i == '{'): stack.append('}') elif (i == '['): stack.append(']') elif (i == '('): stack.append(')') else: if (stack == [] or i != stack[-1]): return False stack.pop(); return stack ==[] t = int(input().strip()) for x in range(t): expression = input().strip() if is_matched(expression) == True: print("YES") else: print("NO")

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