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SOFT Core
SOFT 260
Graph Search in Class
Commits
3f4515c6
Commit
3f4515c6
authored
Oct 6, 2022
by
Brady James Garvin
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Designed, traced, and coded DFS.
parent
6500808f
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graph-search/notes.md
+20
-5
20 additions, 5 deletions
graph-search/notes.md
graph-search/src/features/search/search.js
+25
-19
25 additions, 19 deletions
graph-search/src/features/search/search.js
with
45 additions
and
24 deletions
graph-search/notes.md
+
20
−
5
View file @
3f4515c6
...
...
@@ -18,10 +18,16 @@ but it cannot move left, because trying would move it past the end of the string
How many moves does it take to reverse the string
`123`
?
> Four, in one of two ways:
> `123` → `213` → `132` → `312` → `321`
> `123` → `213` → `231` → `312` → `321`
# Problem 2:
In the weighted directed graph on the whiteboard, what is the shortest path from
`a`
to
`d`
?
> a → c → e → f → d (total weight of 14)
---------------------------------------------------------------------
# Worklist Algorithms for Graph Search
...
...
@@ -31,18 +37,27 @@ In the weighted directed graph on the whiteboard, what is the shortest path from
## Depth-First Search (DFS)
*
Worklist:
…
*
Worklist:
Stack
*
Guaranteed to find a path if one exists
*
Not guaranteed to find a good path
*
Can be made very memory efficient (topic for Thursday)
Worklist Backpointers
-------- ------------
(⊥, a)
(⊥, a) ✓ a → (⊥, a)
(a, c) ✓ c → (a, c)
(c, e) b → (c, b)
(c, b) ✓ e → (b, e)
(b, e) ✓ f → (e, f)
(b, a) ✓ d → (f, d)
(e, d)
(e, f) ✓
(f, c)
(f, d) ✓
Reversed Path
----
…
d ← f ← e ← b ← c ← a
## Breadth-First Search (BFS)
...
...
This diff is collapsed.
Click to expand it.
graph-search/src/features/search/search.js
+
25
−
19
View file @
3f4515c6
...
...
@@ -9,25 +9,31 @@ class Edge {
}
export
function
dfs
(
graph
,
source
,
destination
)
{
// // SEARCH:
// // base case
// // initiation
// while (…) { // termination condition
// // consecution (part i)
// // action
// if (…) { // early termination conditional
// // POSTPROCESSING:
// // base case
// for(…; // initiation
// …; // termination condition
// …) { // consecution
// // action
// }
// return …;
// }
// // consecution (part ii)
// }
return
undefined
;
// TODO: stub
// SEARCH:
const
backpointers
=
new
Map
();
const
worklist
=
[];
worklist
.
push
(
new
Edge
(
undefined
,
source
));
while
(
worklist
.
length
>
0
)
{
const
workitem
=
worklist
.
pop
();
if
(
backpointers
.
has
(
workitem
.
to
))
{
continue
;
}
backpointers
.
set
(
workitem
.
to
,
workitem
);
if
(
workitem
.
to
===
destination
)
{
// POSTPROCESSING:
const
reversedPath
=
[];
for
(
let
current
=
destination
;
current
!==
undefined
;
current
=
backpointers
.
get
(
current
).
from
)
{
reversedPath
.
push
(
current
);
}
return
reversedPath
.
reverse
();
}
for
(
const
incidence
of
graph
.
getIncidences
(
workitem
.
to
))
{
worklist
.
push
(
new
Edge
(
workitem
.
to
,
incidence
.
destination
));
}
}
return
undefined
;
}
export
function
bfs
(
graph
,
source
,
destination
)
{
...
...
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