DSA1 | Week 6
Navigating Graphs using BFS
Try them all
Explore one thoroughly
What do you do when you have many different options?
Navigating Graphs
Navigating Graphs
Try them all
Explore one thoroughly
What do you do when you have many different options?
Phase 0.
Identify a
starting point \(s\).
Phase 1.
Collect
all friends of \(s\).
Phase 0.
Identify a
starting point \(s\).
Phase 1.
Collect
all friends of \(s\).
Phase 0.
Identify a
starting point \(s\).
Phase k.
Collect
anyone who is a
friend of
anyone seen before.
\(\cdots\)
\(s\)
\(x\)
\(y\)
\(w\)
\(z\)
\(s\)
\(x\)
\(y\)
\(w\)
\(z\)
\(s\)
\(x\)
\(y\)
\(w\)
\(z\)
\(s\)
\(x\)
\(y\)
\(w\)
\(z\)
Phase 1.
Collect
all friends of \(s\).
Phase 0.
Identify a
starting point \(s\).
Phase k.
Collect
anyone NEW
who is a
friend of
anyone seen before.
\(\cdots\)
Implementation?
ask every unvisited node if
they are adjacent to
any visited node.
Phase #\(k\).
execute_one_round():
for all v in V(G):
if v is not in visited:
for all u in N(v):
if u is in visited:
mark v
add all marked vertices to visited
execute_one_round():
for all v in boundary(G):
for all u in N(v):
if u is unvisited &
has unvisited neighbors:
mark u RED
else if u is unvisited:
mark u BLUE
move boundary to deadzone
add all RED vertices to boundary + visited
add all BLUE vertices to deadzone + visited
visited = [s] repeat n times:
execute_one_round()
visited[s] = true
add s to head of Q
while Q is non-empty:
v = pop(Q) //remove the head of Q
for u in N(v):
if visited[u] is false:
add u to visited and push(Q,u)
0
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
0
01
03
04
05
07
08
09
11
12
13
14
15
16
17
18
19
20
21
22
23
24
0
01
04
05
08
09
12
13
14
16
17
18
19
20
21
22
23
24
2023 DSA 1 | Week 6
By Neeldhara Misra
2023 DSA 1 | Week 6
- 808
