Graph labelling problem has been broadly studied for a long period for its applications, especially in frequency assignment in (mobile) communication system,
X
-ray crystallography, circuit design, etc. Nowadays, surjective
L
2,1
-labelling is a well-studied problem. Motivated from the
L
2,1
-labelling problem and the importance of surjective
L
2,1
-labelling problem, we consider surjective
L
2,1
-labelling (
SL
21
-labelling) problems for paths and interval graphs. For any graph
G
=
V
,
E
, an
SL
21
-labelling is a mapping
φ
:
V
⟶
1,2
,
…
,
n
so that, for every pair of nodes
u
and
v
, if
d
u
,
v
=
1
, then
φ
u
−
φ
v
≥
2
; and if
d
u
,
v
=
2
, then
φ
u
−
φ
v
≥
1
, and every label
1,2
,
…
,
n
is used exactly once, where
d
u
,
v
represents the distance between the nodes
u
and
v
, and
n
is the number of nodes of graph
G
. In the present article, it is proved that any path
P
n
can be surjectively
L
2,1
-labelled if
n
≥
4
, and it is also proved that any interval graph
IG
G
having
n
nodes and degree
Δ
>
2
can be surjectively
L
2,1
-labelled if
n
=
3
Δ
−
1
. Also, we have designed two efficient algorithms for surjective
L
2,1
-labelling of paths and interval graphs. The results regarding both paths and interval graphs are the first result for surjective
L
2,1
-labelling.