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Commit 3f4515c6 authored by Brady James Garvin's avatar Brady James Garvin
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Designed, traced, and coded DFS.

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......@@ -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)
......
......@@ -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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