# Find an equal point in a string of brackets

• Difficulty Level : Medium
• Last Updated : 22 Apr, 2022

Given a string of brackets, the task is to find an index k which decides the number of opening brackets is equal to the number of closing brackets.
The string must be consists of only opening and closing brackets i.e. ‘(‘ and ‘)’.

An equal point is an index such that the number of opening brackets before it is equal to the number of closing brackets from and after.

Examples:

Input: str = “(())))(“
Output:   4
Explanation: After index 4, string splits into (()) and ))(. The number of opening brackets in the first part is equal to the number of closing brackets in the second part.

Input: str = “))”
Output: 2
Explanation: As after 2nd position i.e. )) and “empty” string will be split into these two parts. So, in this number of opening brackets i.e. 0 in the first part is equal to the number of closing brackets in the second part i.e. also 0. Approach 1:

• Store the number of opening brackets appears in the string up to every index, it must start from starting index.
• Similarly, Store the number of closing brackets appears in the string upto each and every index but it should be done from last index.
• Check if any index has the same value of opening and closing brackets.

Below is the implementation of the above approach:

## C++

 `// C++ program to find an index k which``// decides the number of opening brackets``// is equal to the number of closing brackets``#include``using` `namespace` `std;` `// Function to find an equal index``int` `findIndex(string str)``{``    ``int` `len = str.length();``    ``int` `open[len+1], close[len+1];``    ``int` `index = -1;``    ``memset``(open, 0, ``sizeof` `(open));``    ``memset``(close, 0, ``sizeof` `(close));` `    ``open = 0;``    ``close[len] = 0;``    ``if` `(str==``'('``)``        ``open = 1;``    ``if` `(str[len-1] == ``')'``)``        ``close[len-1] = 1;` `    ``// Store the number of opening brackets``    ``// at each index``    ``for` `(``int` `i = 1; i < len; i++)``    ``{``        ``if` `( str[i] == ``'('` `)``            ``open[i+1] = open[i] + 1;``        ``else``            ``open[i+1] = open[i];``    ``}` `    ``// Store the number of closing brackets``    ``// at each index``    ``for` `(``int` `i = len-2; i >= 0; i--)``    ``{``        ``if` `( str[i] == ``')'` `)``            ``close[i] = close[i+1] + 1;``        ``else``            ``close[i] = close[i+1];``    ``}` `    ``// check if there is no opening or closing``    ``// brackets``    ``if` `(open[len] == 0)``        ``return` `len;``    ``if` `(close == 0)``        ``return` `0;` `    ``// check if there is any index at which``    ``// both brackets are equal``    ``for` `(``int` `i=0; i<=len; i++)``        ``if` `(open[i] == close[i])``            ``index = i;` `    ``return` `index;``}` `// Driver code``int` `main()``{``    ``string str = ``"(()))(()()())))"``;``    ``cout << findIndex(str);``    ``return` `0;``}`

## Java

 `// Java program to find an index k which``// decides the number of opening brackets``// is equal to the number of closing brackets` `public` `class` `GFG``{``    ``// Method to find an equal index``    ``static` `int` `findIndex(String str)``    ``{``        ``int` `len = str.length();``        ``int` `open[] = ``new` `int``[len+``1``];``        ``int`    `close[] = ``new` `int``[len+``1``];``        ``int` `index = -``1``;``     ` `        ``open[``0``] = ``0``;``        ``close[len] = ``0``;``        ``if` `(str.charAt(``0``)==``'('``)``            ``open[``1``] = ``1``;``        ``if` `(str.charAt(len-``1``) == ``')'``)``            ``close[len-``1``] = ``1``;``     ` `        ``// Store the number of opening brackets``        ``// at each index``        ``for` `(``int` `i = ``1``; i < len; i++)``        ``{``            ``if` `( str.charAt(i) == ``'('` `)``                ``open[i+``1``] = open[i] + ``1``;``            ``else``                ``open[i+``1``] = open[i];``        ``}``     ` `        ``// Store the number of closing brackets``        ``// at each index``        ``for` `(``int` `i = len-``2``; i >= ``0``; i--)``        ``{``            ``if` `( str.charAt(i) == ``')'` `)``                ``close[i] = close[i+``1``] + ``1``;``            ``else``                ``close[i] = close[i+``1``];``        ``}``     ` `        ``// check if there is no opening or closing``        ``// brackets``        ``if` `(open[len] == ``0``)``            ``return` `len;``        ``if` `(close[``0``] == ``0``)``            ``return` `0``;``    ` `        ``// check if there is any index at which``        ``// both brackets are equal``        ``for` `(``int` `i=``0``; i<=len; i++)``            ``if` `(open[i] == close[i])``                ``index = i;``     ` `        ``return` `index;``    ``}``    ` `    ``// Driver Method``    ``public` `static` `void` `main(String[] args)``    ``{``        ``String str = ``"(()))(()()())))"``;``        ``System.out.println(findIndex(str));``    ``}``}`

## Python3

 `# Method to find an equal index``def` `findIndex(``str``):``    ``l ``=` `len``(``str``)``    ``open` `=` `[``0``] ``*` `(l ``+` `1``)``    ``close ``=` `[``0``] ``*` `(l ``+` `1``)``    ``index ``=` `-``1``    ` `    ``open``[``0``] ``=` `0``    ``close[l] ``=` `0``    ``if` `(``str``[``0``]``=``=``'('``):``        ``open``[``1``] ``=` `1``    ``if` `(``str``[l ``-` `1``] ``=``=` `')'``):``        ``close[l ``-` `1``] ``=` `1``    ` `    ``# Store the number of``    ``# opening brackets``    ``# at each index``    ``for` `i ``in` `range``(``1``, l):``        ``if` `(``str``[i] ``=``=` `'('``):``            ``open``[i ``+` `1``] ``=` `open``[i] ``+` `1``        ``else``:``            ``open``[i ``+` `1``] ``=` `open``[i]``    ` `    ``# Store the number``    ``# of closing brackets``    ``# at each index``    ``for` `i ``in` `range``(l ``-` `2``, ``-``1``, ``-``1``):``        ``if` `( ``str``[i] ``=``=` `')'``):``            ``close[i] ``=` `close[i ``+` `1``] ``+` `1``        ``else``:``            ``close[i] ``=` `close[i ``+` `1``]``    ` `    ``# check if there is no``    ``# opening or closing brackets``    ``if` `(``open``[l] ``=``=` `0``):``        ``return` `len``    ``if` `(close[``0``] ``=``=` `0``):``        ``return` `0``    ` `    ``# check if there is any``    ``# index at which both``    ``# brackets are equal``    ``for` `i ``in` `range``(l ``+` `1``):``        ``if` `(``open``[i] ``=``=` `close[i]):``            ``index ``=` `i``    ` `    ``return` `index``    ` `# Driver Code``str` `=` `"(()))(()()())))"``print``(findIndex(``str``))` `# This code is contributed``# by ChitraNayal`

## C#

 `// C# program to find an index``// k which decides the number``// of opening brackets is equal``// to the number of closing brackets``using` `System;` `class` `GFG``{``// Method to find an equal index``static` `int` `findIndex(``string` `str)``{``    ``int` `len = str.Length;``    ``int``[] open = ``new` `int``[len + 1];``    ``int``[] close = ``new` `int``[len + 1];``    ``int` `index = -1;` `    ``open = 0;``    ``close[len] = 0;``    ``if` `(str == ``'('``)``        ``open = 1;``    ``if` `(str[len - 1] == ``')'``)``        ``close[len - 1] = 1;` `    ``// Store the number of``    ``// opening brackets``    ``// at each index``    ``for` `(``int` `i = 1; i < len; i++)``    ``{``        ``if` `(str[i] == ``'('``)``            ``open[i + 1] = open[i] + 1;``        ``else``            ``open[i + 1] = open[i];``    ``}` `    ``// Store the number``    ``// of closing brackets``    ``// at each index``    ``for` `(``int` `i = len - 2; i >= 0; i--)``    ``{``        ``if` `(str[i] == ``')'``)``            ``close[i] = close[i + 1] + 1;``        ``else``            ``close[i] = close[i + 1];``    ``}` `    ``// check if there is no``    ``// opening or closing``    ``// brackets``    ``if` `(open[len] == 0)``        ``return` `len;``    ``if` `(close == 0)``        ``return` `0;` `    ``// check if there is any``    ``// index at which both``    ``// brackets are equal``    ``for` `(``int` `i = 0; i <= len; i++)``        ``if` `(open[i] == close[i])``            ``index = i;` `    ``return` `index;``}` `// Driver Code``public` `static` `void` `Main()``{``    ``string` `str = ``"(()))(()()())))"``;``    ``Console.Write(findIndex(str));``}``}` `// This code is contributed``// by ChitraNayal`

## PHP

 `= 0; ``\$i``--)``    ``{``        ``if` `(``\$str``[``\$i``] == ``')'``)``        ``\$close``[``\$i``] = ``\$close``[``\$i` `+ 1] + 1;``        ``else``        ``\$close``[``\$i``] = ``\$close``[``\$i` `+ 1];``    ``}``    ` `    ``// check if there is no``    ``// opening or closing``    ``// brackets``    ``if` `(``\$open``[``\$len``] == 0)``        ``return` `\$len``;``    ``if` `(``\$close`` == 0)``        ``return` `0;``    ` `    ``// check if there is any``    ``// index at which both``    ``// brackets are equal``    ``for` `(``\$i` `= 0; ``\$i` `<= ``\$len``; ``\$i``++)``        ``if` `(``\$open``[``\$i``] == ``\$close``[``\$i``])``            ``\$index` `= ``\$i``;``    ` `    ``return` `\$index``;``}``    ` `// Driver Code``\$str` `= ``"(()))(()()())))"``;``echo` `(findIndex(``\$str``));` `// This code is contributed``// by ChitraNayal``?>`

## Javascript

 ``
Output
`9`

Time Complexity: O(N), where N is the size of given string
Auxiliary Space: O(N)

Approach 2:

• Count the total number of closed brackets in string and store in variable, let’s say cnt_close.
• So count of open brackets is length of (string – count) of closed brackets.
• Traverse string again but now keep count of open brackets in string, let’s say cnt_open.
• Now while traversing, let index be i, so count of closed brackets till that index will be (i+1 – cnt_open).
• Hence, we can check for what index, the count of open brackets in first part equals that of count of closed brackets in second part.
• Equation becomes cnt_close – (i+1 – cnt_open) = cnt_open, we have to find i.
• After evaluating above equation we can see cnt_open gets cancelled on both sides so no need.

## C++

 `// C++ program to find an index k which``// decides the number of opening brackets``// is equal to the number of closing brackets``#include ``using` `namespace` `std;` `// Function to find an equal index``int` `findIndex(string str)``{``    ``// STL to count occurrences of ')'``    ``int` `cnt_close = count(str.begin(), str.end(), ``')'``);``    ``for` `(``int` `i = 0; str[i] != ``'\0'``; i++)``        ``if` `(cnt_close == i)``            ``return` `i;``    ``// If no opening brackets``    ``return` `str.size();``}` `// Driver code``int` `main()``{``    ``string str = ``"(()))(()()())))"``;``    ``cout << findIndex(str);``    ``return` `0;``}` `// This code is contributed by Dhananjay Dhawale @chessnoobdj`

## Java

 `// Java program to find an index k which``// decides the number of opening brackets``// is equal to the number of closing brackets` `public` `class` `GFG {``    ``// Method to find an equal index``    ``static` `int` `findIndex(String str)``    ``{``        ``int` `len = str.length();``        ``int` `cnt_close = ``0``;``        ``for` `(``int` `i = ``0``; i < len; i++)``            ``if` `(str.charAt(i) == ``')'``)``                ``cnt_close++;``        ``for` `(``int` `i = ``0``; i < len; i++)``            ``if` `(cnt_close == i)``                ``return` `i;``        ``// If no opening brackets``        ``return` `len;``    ``}` `    ``// Driver Method``    ``public` `static` `void` `main(String[] args)``    ``{``        ``String str = ``"(()))(()()())))"``;``        ``System.out.println(findIndex(str));``    ``}``}` `// This code is contributed by Aditya Kumar (adityakumar129)`

## Python3

 `# Method to find an equal index``def` `findIndex(``str``):``    ``cnt_close ``=` `0``    ``l ``=` `len``(``str``)``    ``for` `i ``in` `range``(``1``, l):``        ``if``(``str``[i] ``=``=` `')'``):``            ``cnt_close ``=` `cnt_close ``+` `1` `    ``for` `i ``in` `range``(``1``, l):``        ``if``(cnt_close ``=``=` `i):``            ``return` `i``    ``# If no opening brackets``    ``return` `l`  `# Driver Code``str` `=` `"(()))(()()())))"``print``(findIndex(``str``))` `# This code is contributed by Aditya Kumar (adityakumar129)`

## Javascript

 ``

## PHP

 ``
Output
`9`

Time Complexity: O(N), Where N is the size of given string
Auxiliary Space: O(1)

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