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1.
Singapore and Malaysia
Connect by bridge ove the Johor Strait
2.
Papua New Guinea and East Timor
PNG borders Indonesia in the New Guinea Island and East Timor borders Indonesia in the Timor Island
4.
Liechtenstein and Germany
Liechtenstein is landlocked by Switzerland and Austria
5.
Denmark and Sweden
Only sea border
6.
Spain and Morocco
Ceuta, Melila and other colonial possessions of spain border Morocco
7.
Brunei and Indonesia
Brunei borders Malaysia on the Borneo Island
8.
Saudi Arabia and Bahrain
Connect by bridge
10.
Namibia and Zimbabwe
Both border Botswana and Zambia on the Zambezi river but they don't quite border each other
11.
Norway and Russia
On the very north of both countries
12.
Serbia and Albania
Going by the JetPunk recognized countries. Serbia and Albania are separeted by Kosovo
13.
United Kingdom and Spain
Gibraltar on the south of Spain is part of the UK
15.
North Korea and China