Problem 111. Find matching parenthesis

Created by Aleksey

Solve Later

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One of the most indispensable things about a great text editor for programming is the ability to quickly jump between matching parentheses. If you have a line like,<pre> if (f(a) >= b(c, d(e*(f-g))))</pre>it very convenient to place your cursor at, say, the second to last closing parenthesis, and have the editor show you where is the matching opening parenthesis. (In this example, it is the one just after <tt>b</tt>.)For this problem, you should write a function that takes a string <tt>s</tt> like <tt>'if (f(a) >= b(c, d(e*f(-g))))'</tt> and an integer <tt>n</tt> representing a character position within the string. Your function should return the index of the matching parenthesis.For example:<pre> >> s = 'if (f(a) >= b(c, d(e*f(-g))))';</pre><pre> >> find_matching_paren(s, 4)</pre><pre> ans =</pre><pre> 29</pre><pre> >> find_matching_paren(s, 6)</pre><pre> ans =</pre><pre> 8</pre><pre> >> find_matching_paren(s, 27)</pre><pre> ans =</pre><pre> 19</pre>You can assume that <tt>n</tt> will always be the position of either an open or closing parenthesis.You can assume the string will always have balanced parentheses.

One of the most indispensable things about a great text editor for programming is the ability to quickly jump between matching parentheses.  If you have a line like,

if (f(a) >= b(c, d(e*(f-g))))

it very convenient to place your cursor at, say, the second to last closing parenthesis, and have the editor show you where is the matching opening parenthesis.  (In this example, it is the one just after |b|.)

For example:

>> s = 'if (f(a) >= b(c, d(e*f(-g))))';
    
    >> find_matching_paren(s, 4)
    
    ans =
    
        29
    
    >> find_matching_paren(s, 6)
    
    ans =
    
         8
    
    >> find_matching_paren(s, 27)
    
    ans =
    
        19

You can assume that |n| will always be the position of either an open or closing parenthesis.

You can assume the string will always have balanced parentheses.

Solve

Solution Stats

632 Solutions
191 Solvers

Last Solution submitted on Jan 18, 2022

Last 200 Solutions

Problem Comments

3 Comments

3 Comments

Qianqian Fang on 6 May 2019

wondering if there is a place I can review the submitted solution source codes? I think this is a great place to learn about matlab programming.

goc3 on 17 May 2019

@Qianqian Fang: once you've solved a problem, click on the solution map (containing all the green circles and orange x's). On that separate page you can click on each of the shapes to view each solution below the chart.

Nikolaos Nikolaou on 30 Jul 2019

somehow i get that s='()' is there something wrong with the test suite?

Solution Comments

Solution 1470243

1 Comment

1 Comment

Da Lu on 24 Mar 2018

第一次解决问题时，想了很长时间....然并卵
第二次看这个问题，十分钟内解决

Solution 322639

1 Comment

1 Comment

Jan Orwat on 23 Sep 2013

It is curious that many solutions checks the "direction" of given parenthesis to find it's pair.

Solution 140433

1 Comment

1 Comment

Aurelien Queffurust on 29 Nov 2012

wow I don't find the words to comment this solution except who can read that?!!

Solution 140318

2 Comments

2 Comments

Jean-Marie Sainthillier on 29 Apr 2014

Wonderful solution.
Technically, I don't understand where ans is created. If I break this code, I obtain an error (ans is undefined). It seems that the line 4 create ans but only in the function (?).

Khaled Hamed on 30 Apr 2014

Hi Jean-Marie. I haven't bee around for some time now. Well, that turned out to be a bug...
http://www.mathworks.com/matlabcentral/answers/46972-is-this-a-possible-matlab-bug-further-strange-behavior

Solution 107122

1 Comment

1 Comment

Jean-Marie Sainthillier on 5 Jul 2013

Brilliant !!!

Solution 6797

1 Comment

1 Comment

Patrick Kalita on 26 Jan 2012

vectors, schmectors!

Problem Recent Solvers191

Problem Tags

parens parentheses

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