feat: add solutions to lc problem: No.3438

[yanglbme]

No.3438.Find Valid Pair of Adjacent Digits in String

[idoocs]

Images automagically compressed by Calibre's image-actions ✨

Compression reduced images by 85.9%, saving 51.42 KB.

Filename	Before	After	Improvement	Visual comparison
solution/3400-3499/3439.Reschedule Meetings for Maximum Free Time I/images/example0_rescheduled.png	9.71 KB	1.45 KB	-85.1%	View diff
solution/3400-3499/3439.Reschedule Meetings for Maximum Free Time I/images/example1_rescheduled.png	13.25 KB	1.82 KB	-86.3%	View diff
solution/3400-3499/3440.Reschedule Meetings for Maximum Free Time II/images/example0_rescheduled.png	9.71 KB	1.45 KB	-85.1%	View diff
solution/3400-3499/3440.Reschedule Meetings for Maximum Free Time II/images/image3.png	13.88 KB	1.89 KB	-86.4%	View diff
solution/3400-3499/3440.Reschedule Meetings for Maximum Free Time II/images/rescheduled_example0.png	13.28 KB	1.80 KB	-86.5%	View diff

2021 images did not require optimisation.