Here's a Freebie, it is marked as "Easy"
This problem was asked by Facebook.
Given a string of round, curly, and square open and closing brackets, return whether the brackets are balanced (well-formed).
For example, given the string "([])[]({})", you should return true.
Given the string "([)]" or "((()", you should return false.
Octave solution
Should be fairly easy to modify for other bracket types, just add them to the lists at the top and bottom (using the same index for an open bracket and its corresponding close bracket).
function valid = is_balanced(string)
open_brackets = '({[';
close_brackets = ')}]';
expecting = false(size(string));
valid = true;
expected_bracket = [];
for index = 1:numel(string)
if ismember(string(index), open_brackets)
expecting(index) = true;
expected_bracket = strchr(open_brackets, string(index));
elseif ismember(string(index), close_brackets)
if expected_bracket == strchr(close_brackets, string(index))
expecting(find(expecting, 1, 'last')) = false;
expected_bracket = strchr(open_brackets, string(find(expecting, 1, 'last')));
else
valid = false; end; end; end;
if any(expecting)
valid = false; end; end;
