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Commit 8bd2a1ec authored by Brady James Garvin's avatar Brady James Garvin
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Traced BeFS and recursive DFS, implemented BeFS, and discussed admissibility.

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...@@ -113,24 +113,34 @@ Four moves: `123` → `213` → `231` → `312` → `321` ...@@ -113,24 +113,34 @@ Four moves: `123` → `213` → `231` → `312` → `321`
------------ -------------- ------------ --------------
(⊥, a, 0) → 2 ✓ a → (⊥, a, 0) (⊥, a, 0) → 2 ✓ a → (⊥, a, 0)
(a, c, 7) → 9 ✓ c → (a, c, 7) (a, c, 7) → 9 ✓ c → (a, c, 7)
(c, e, 12) → 13 (c, e, 12) → 13 ✓ b → (c, b, 8)
(c, b, 8) → 9 (c, b, 8) → 9 ✓ e → (c, e, 12)
(b, e, 17) → 18 d → (e, d, 15)
(b, a, 12) → 14 ✓
(e, d, 15) → 15 ✓
(e, f, 14) → 16
Reversed Path Reversed Path
---- ----
d ← e ← c ← a
## A* ## A*
* Worklist: * Worklist: Priority Queue
* Priority: * Priority: Distance travelled from the source plus estimated distance to the destination (using an *admissible* heuristic)
* Guaranteed to find a path with least weight * Guaranteed to find a path with least weight
* Can have good best- and average-case time efficiency * Can have good best- and average-case time efficiency
## Recursive Depth-First Search (DFS) ## Recursive Depth-First Search (DFS)
* Worklist: * Worklist: The program stack
Activation Frames Backpointers Returned Activation Frames Backpointers Returned
----------------------------------- ------------ ---------------- ----------------------------------- ------------ ----------------
edge = (⊥, a), incidence = … edge = (⊥, a), incidence = (a, c) a → (⊥, a) [a, c, b, e, f, d]
edge = (a, c), incidence = (c, b) c → (a, c) [c, b, e, f, d]
edge = (c, b), incidence = (b, e) b → (c, b) [b, e, f, d]
edge = (b, a) ⊥
edge = (b, e), incidence = (e, f) e → (b, e) [e, f, d]
edge = (e, f), incidence = (f, d) f → (e, f) [f, d]
edge = (f, d) d → (f, d) [d]
...@@ -90,11 +90,43 @@ export function dijkstras(graph, source, destination) { ...@@ -90,11 +90,43 @@ export function dijkstras(graph, source, destination) {
} }
function heuristic(vertex, destination) { function heuristic(vertex, destination) {
return 0; // TODO: stub if ('acf'.includes(vertex)) {
return 2;
}
if ('be'.includes(vertex)) {
return 1;
}
return 0;
} }
export function bestFirst(graph, source, destination) { export function bestFirst(graph, source, destination) {
return undefined; // TODO: stub const backpointers = new Map();
const worklist = new PriorityQueue();
worklist.insert(new Edge(undefined, source, 0), heuristic(source, destination));
while (worklist.size > 0) {
const workitem = worklist.remove();
if (backpointers.has(workitem.to) &&
backpointers.get(workitem.to).distance <= workitem.distance) {
continue;
}
backpointers.set(workitem.to, workitem);
if (workitem.to === destination) {
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.insert(
new Edge(workitem.to, incidence.destination, workitem.distance + incidence.weight),
workitem.distance + incidence.weight + heuristic(incidence.destination, destination),
);
}
}
return undefined;
} }
export function recursiveDFS(graph, source, destination) { export function recursiveDFS(graph, source, destination) {
......
...@@ -29,7 +29,7 @@ function formatSolution(solution) { ...@@ -29,7 +29,7 @@ function formatSolution(solution) {
} }
export function Solution(props) { export function Solution(props) {
const search = dijkstras; const search = bestFirst;
const firstSolution = search(firstExample, 'a', 'd'); const firstSolution = search(firstExample, 'a', 'd');
const secondSolution = search(secondExample, '123', '321'); const secondSolution = search(secondExample, '123', '321');
return ( return (
......
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