Start from (1). Visit every destination. It is not necessary to return to (1).
Visually:
(3) 13 (2)
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|\ /|
| \ / |
| \ / |
| \ / |
| \ 12 / |
| \ / |
| \ / |
| \ / |
10 | \ / | 20
| \ / |
| \/ |
| /\ |
| / \ |
| / \ |
| / \ |
| / \ |
| / 11 \ |
| / \ |
| / \ |
| / \ |
| / \ |
|/ \|
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(1) 14 (4)
CSV:
from,to,distance
1,2,11
1,3,10
1,4,14
2,1,11
2,3,13
2,4,20
3,1,10
3,2,13
3,4,12
4,1,14
4,2,20
4,3,12