From d2aa9289c5c3a2fa2b6442bea771f6578624e3eb Mon Sep 17 00:00:00 2001
From: "Brady J. Garvin" <bgarvin@cse.unl.edu>
Date: Fri, 20 Oct 2023 14:35:10 -0500
Subject: [PATCH] Took notes from Wednesday.
---
greedy-algorithms/notes.md | 4 +++-
.../src/features/encoding/solver.js | 19 ++++++++++++++++++-
2 files changed, 21 insertions(+), 2 deletions(-)
diff --git a/greedy-algorithms/notes.md b/greedy-algorithms/notes.md
index 2e3a406..17d5fa4 100644
--- a/greedy-algorithms/notes.md
+++ b/greedy-algorithms/notes.md
@@ -240,4 +240,6 @@ Problem: Given frequencies for a set of symbols, create a lossless binary encodi
Symbol Partitioning (Frequency Order) 'a' 'b' 'c' 'd'
------------------------------------------------------- --- --- --- ---
{'a'} → 0.15, {'c'} → 0.25, {'b'} → 0.30, {'d'} → 0.30
- …
+ {'a', 'c'} → 0.40, {'b'} → 0.30, {'d'} → 0.30 0 1
+ {'a', 'c'} → 0.40, {'b', 'd'} → 0.60 0 0 1 1
+ {'a', 'c', 'b', 'd'} → 1.00 00 10 01 11
diff --git a/greedy-algorithms/src/features/encoding/solver.js b/greedy-algorithms/src/features/encoding/solver.js
index 7c7344b..ffa56ad 100644
--- a/greedy-algorithms/src/features/encoding/solver.js
+++ b/greedy-algorithms/src/features/encoding/solver.js
@@ -1,8 +1,25 @@
+import { PriorityQueue } from './collections.js';
+
export function findEncoding(frequencies) {
const results = new Map();
+ const partitioning = new PriorityQueue();
for (const [meaning, frequency] of frequencies) {
results.set(meaning, '');
+ partitioning.insert(new Set([meaning]), frequency);
+ }
+ while (partitioning.size > 1) {
+ const [firstMeaningSet, firstFrequency] = partitioning.remove();
+ const [secondMeaningSet, secondFrequency] = partitioning.remove();
+ for (const meaning of firstMeaningSet) {
+ results.set(meaning, `0${results.get(meaning)}`);
+ }
+ for (const meaning of secondMeaningSet) {
+ results.set(meaning, `1${results.get(meaning)}`);
+ }
+ partitioning.insert(
+ new Set([...firstMeaningSet, ...secondMeaningSet]),
+ firstFrequency + secondFrequency,
+ );
}
- // TODO: stub
return results;
}
--
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