10
[Hard] Longest Valid Bracket Pattern
(programming.dev)
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Easy challenges will give 1 point, medium will give 2, and hard will give 3. If you have the fastest time or use the least amount of characters you will get a bonus point (in ties everyone gets the bonus point)
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C:
gcc -O2 hard.c
This is very poorly written, but does seem to work.
The stack keeps track of the start of a match, and the character that would complete the match. In cases where a match just ended, the start is preserved (because two adjacent matches are effectively one), but the required matching character is changed to that of the new opening match.