# Expression contains redundant bracket or not

• Difficulty Level : Medium
• Last Updated : 22 Oct, 2021

Given a string of balanced expression, find if it contains a redundant parenthesis or not. A set of parenthesis are redundant if the same sub-expression is surrounded by unnecessary or multiple brackets. Print ‘Yes’ if redundant, else ‘No’.
Note: Expression may contain ‘+‘, ‘*‘, ‘‘ and ‘/‘ operators. Given expression is valid and there are no white spaces present.
Example:

```Input:
((a+b))
(a+(b)/c)
(a+b*(c-d))
Output:
Yes
Yes
No

Explanation:
1. ((a+b)) can reduced to (a+b), this Redundant
2. (a+(b)/c) can reduced to (a+b/c) because b is
surrounded by () which is redundant.
3. (a+b*(c-d)) doesn't have any redundant or multiple
brackets.```

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The idea is to use stack, which is discussed in this article. For any sub-expression of expression, if we are able to pick any sub-expression of expression surrounded by (), then we again left with () as part of string, we have redundant braces.
We iterate through the given expression and for each character in the expression, if the character is an open parenthesis ‘(‘ or any of the operators or operands, we push it to the stack. If the character is close parenthesis ‘)’, then pop characters from the stack till matching open parenthesis ‘(‘ is found.
Now for redundancy two condition will arise while popping-

1. If immediate pop hits an open parenthesis ‘(‘, then we have found a duplicate parenthesis. For example, (((a+b))+c) has duplicate brackets around a+b. When we reach the second “)” after a+b, we have “((” in the stack. Since the top of stack is an opening bracket, we conclude that there are duplicate brackets.

2. If immediate pop doesn’t hit any operand(‘*’, ‘+’, ‘/’, ‘-‘) then it indicates the presence of unwanted brackets surrounded by expression. For instance, (a)+b contain unwanted () around a thus it is redundant.

## C++

 `/* C++ Program to check whether valid`` ``expression is redundant or not*/``#include ``using` `namespace` `std;` `// Function to check redundant brackets in a``// balanced expression``bool` `checkRedundancy(string& str)``{``    ``// create a stack of characters``    ``stack<``char``> st;` `    ``// Iterate through the given expression``    ``for` `(``auto``& ch : str) {` `        ``// if current character is close parenthesis ')'``        ``if` `(ch == ``')'``) {``            ``char` `top = st.top();``            ``st.pop();` `            ``// If immediate pop have open parenthesis '('``            ``// duplicate brackets found``            ``bool` `flag = ``true``;` `            ``while` `(!st.empty() and top != ``'('``) {` `                ``// Check for operators in expression``                ``if` `(top == ``'+'` `|| top == ``'-'` `||``                    ``top == ``'*'` `|| top == ``'/'``)``                    ``flag = ``false``;` `                ``// Fetch top element of stack``                ``top = st.top();``                ``st.pop();``            ``}` `            ``// If operators not found``            ``if` `(flag == ``true``)``                ``return` `true``;``        ``}` `        ``else``            ``st.push(ch); ``// push open parenthesis '(',``                  ``// operators and operands to stack``    ``}``    ``return` `false``;``}` `// Function to check redundant brackets``void` `findRedundant(string& str)``{``    ``bool` `ans = checkRedundancy(str);``    ``if` `(ans == ``true``)``        ``cout << ``"Yes\n"``;``    ``else``        ``cout << ``"No\n"``;``}` `// Driver code``int` `main()``{``    ``string str = ``"((b*c)*(a/b))"``;``    ``findRedundant(str);` `    ``str = ``"(a+(b)/c)"``;``    ``findRedundant(str);` `    ``str = ``"(a+b*(c-d))"``;``    ``findRedundant(str);` `    ``return` `0;``}`

## Java

 `/* Java Program to check whether valid``expression is redundant or not*/``import` `java.util.Stack;``public` `class` `GFG {``// Function to check redundant brackets in a``// balanced expression` `    ``static` `boolean` `checkRedundancy(String s) {``        ``// create a stack of characters``        ``Stack st = ``new` `Stack<>();``        ``char``[] str = s.toCharArray();``        ``// Iterate through the given expression``        ``for` `(``char` `ch : str) {` `            ``// if current character is close parenthesis ')'``            ``if` `(ch == ``')'``) {``                ``char` `top = st.peek();``                ``st.pop();` `                ``// If immediate pop have open parenthesis '('``                ``// duplicate brackets found``                ``boolean` `flag = ``true``;` `                ``while` `(top != ``'('``) {` `                    ``// Check for operators in expression``                    ``if` `(top == ``'+'` `|| top == ``'-'``                            ``|| top == ``'*'` `|| top == ``'/'``) {``                        ``flag = ``false``;``                    ``}` `                    ``// Fetch top element of stack``                    ``top = st.peek();``                    ``st.pop();``                ``}` `                ``// If operators not found``                ``if` `(flag == ``true``) {``                    ``return` `true``;``                ``}``            ``} ``else` `{``                ``st.push(ch); ``// push open parenthesis '(',``            ``}                ``// operators and operands to stack``        ``}``        ``return` `false``;``    ``}` `// Function to check redundant brackets``    ``static` `void` `findRedundant(String str) {``        ``boolean` `ans = checkRedundancy(str);``        ``if` `(ans == ``true``) {``            ``System.out.println(``"Yes"``);``        ``} ``else` `{``            ``System.out.println(``"No"``);``        ``}``    ``}` `// Driver code``    ``public` `static` `void` `main(String[] args) {``        ``String str = ``"((a+b))"``;``        ``findRedundant(str);` `        ``str = ``"(a+(b)/c)"``;``        ``findRedundant(str);` `        ``str = ``"(a+b*(c-d))"``;``        ``findRedundant(str);``    ``}``}`

## Python3

 `# Python3 Program to check whether valid``# expression is redundant or not` `# Function to check redundant brackets``# in a balanced expression``def` `checkRedundancy(``Str``):``    ` `    ``# create a stack of characters``    ``st ``=` `[]` `    ``# Iterate through the given expression``    ``for` `ch ``in` `Str``:` `        ``# if current character is close``        ``# parenthesis ')'``        ``if` `(ch ``=``=` `')'``):``            ``top ``=` `st[``-``1``]``            ``st.pop()` `            ``# If immediate pop have open parenthesis``            ``# '(' duplicate brackets found``            ``flag ``=` `True` `            ``while` `(top !``=` `'('``):` `                ``# Check for operators in expression``                ``if` `(top ``=``=` `'+'` `or` `top ``=``=` `'-'` `or``                    ``top ``=``=` `'*'` `or` `top ``=``=` `'/'``):``                    ``flag ``=` `False` `                ``# Fetch top element of stack``                ``top ``=` `st[``-``1``]``                ``st.pop()` `            ``# If operators not found``            ``if` `(flag ``=``=` `True``):``                ``return` `True` `        ``else``:``            ``st.append(ch) ``# append open parenthesis '(',``                          ``# operators and operands to stack``    ``return` `False` `# Function to check redundant brackets``def` `findRedundant(``Str``):``    ``ans ``=` `checkRedundancy(``Str``)``    ``if` `(ans ``=``=` `True``):``        ``print``(``"Yes"``)``    ``else``:``        ``print``(``"No"``)` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``Str` `=` `"((a+b))"``    ``findRedundant(``Str``)` `    ``Str` `=` `"(a+(b)/c)"``    ``findRedundant(``Str``)` `    ``Str` `=` `"(a+b*(c-d))"``    ``findRedundant(``Str``)` `# This code is contributed by PranchalK`

## C#

 `/* C# Program to check whether valid``expression is redundant or not*/``using` `System;``using` `System.Collections.Generic;` `class` `GFG``{``    ``// Function to check redundant brackets in a``    ``// balanced expression``    ``static` `bool` `checkRedundancy(String s)``    ``{``        ``// create a stack of characters``        ``Stack<``char``> st = ``new` `Stack<``char``>();``        ``char``[] str = s.ToCharArray();``        ` `        ``// Iterate through the given expression``        ``foreach` `(``char` `ch ``in` `str)``        ``{` `            ``// if current character is close parenthesis ')'``            ``if` `(ch == ``')'``)``            ``{``                ``char` `top = st.Peek();``                ``st.Pop();` `                ``// If immediate pop have open parenthesis '('``                ``// duplicate brackets found``                ``bool` `flag = ``true``;` `                ``while` `(top != ``'('``)``                ``{` `                    ``// Check for operators in expression``                    ``if` `(top == ``'+'` `|| top == ``'-'``                            ``|| top == ``'*'` `|| top == ``'/'``)``                    ``{``                        ``flag = ``false``;``                    ``}` `                    ``// Fetch top element of stack``                    ``top = st.Peek();``                    ``st.Pop();``                ``}` `                ``// If operators not found``                ``if` `(flag == ``true``)``                ``{``                    ``return` `true``;``                ``}``            ``}``            ``else``            ``{``                ``st.Push(ch); ``// push open parenthesis '(',``            ``}         ``// operators and operands to stack``        ``}``        ``return` `false``;``    ``}` `    ``// Function to check redundant brackets``    ``static` `void` `findRedundant(String str)``    ``{``        ``bool` `ans = checkRedundancy(str);``        ``if` `(ans == ``true``)``        ``{``            ``Console.WriteLine(``"Yes"``);``        ``}``        ``else``        ``{``            ``Console.WriteLine(``"No"``);``        ``}``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``String str = ``"((a+b))"``;``        ``findRedundant(str);` `        ``str = ``"(a+(b)/c)"``;``        ``findRedundant(str);` `        ``str = ``"(a+b*(c-d))"``;``        ``findRedundant(str);``    ``}``}` `/* This code contributed by PrinciRaj1992 */`

## Javascript

 ``
Output
```Yes
Yes
No```

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