Skip to content
Snippets Groups Projects
Commit 3f4515c6 authored by Brady James Garvin's avatar Brady James Garvin
Browse files

Designed, traced, and coded DFS.

parent 6500808f
Branches
No related tags found
No related merge requests found
...@@ -18,10 +18,16 @@ but it cannot move left, because trying would move it past the end of the string ...@@ -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`? 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: # Problem 2:
In the weighted directed graph on the whiteboard, what is the shortest path from `a` to `d`? 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 # Worklist Algorithms for Graph Search
...@@ -31,18 +37,27 @@ In the weighted directed graph on the whiteboard, what is the shortest path from ...@@ -31,18 +37,27 @@ In the weighted directed graph on the whiteboard, what is the shortest path from
## Depth-First Search (DFS) ## Depth-First Search (DFS)
* Worklist: * Worklist: Stack
* Guaranteed to find a path if one exists * Guaranteed to find a path if one exists
* Not guaranteed to find a good path * Not guaranteed to find a good path
* Can be made very memory efficient (topic for Thursday) * Can be made very memory efficient (topic for Thursday)
Worklist Backpointers 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 Reversed Path
---- ----
d ← f ← e ← b ← c ← a
## Breadth-First Search (BFS) ## Breadth-First Search (BFS)
......
...@@ -9,25 +9,31 @@ class Edge { ...@@ -9,25 +9,31 @@ class Edge {
} }
export function dfs(graph, source, destination) { export function dfs(graph, source, destination) {
// // SEARCH: // SEARCH:
// // base case const backpointers = new Map();
// // initiation const worklist = [];
// while (…) { // termination condition worklist.push(new Edge(undefined, source));
// // consecution (part i) while (worklist.length > 0) {
// // action const workitem = worklist.pop();
// if (…) { // early termination conditional if (backpointers.has(workitem.to)) {
// // POSTPROCESSING: continue;
// // base case }
// for(…; // initiation backpointers.set(workitem.to, workitem);
// …; // termination condition if (workitem.to === destination) {
// …) { // consecution // POSTPROCESSING:
// // action const reversedPath = [];
// } for (let current = destination;
// return …; current !== undefined;
// } current = backpointers.get(current).from) {
// // consecution (part ii) reversedPath.push(current);
// } }
return undefined; // TODO: stub 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) { export function bfs(graph, source, destination) {
......
0% Loading or .
You are about to add 0 people to the discussion. Proceed with caution.
Please register or to comment