Huffman encoding Kotlin implementation #640
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neverix
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berquist
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berquist
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May 24, 2020
| class Leaf(freq: Int, val letter: Char): Node(freq) | ||
| class Branch(freq: Int, val left: Node, val right: Node): Node(freq) | ||
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| class HuffmanTree (val textSample: String) { |
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Suggested change
| class HuffmanTree (val textSample: String) { | |
| class HuffmanTree (textSample: String) { |
| @@ -0,0 +1,130 @@ | |||
| import java.util.* | |||
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| // node type | |||
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This comment doesn't really add anything.
| val sourceText = "bibbity_bobbity" | ||
| // create huffman tree | ||
| val huffmanTree = HuffmanTree(sourceText) | ||
| // encode the text |
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This and the above comment aren't very useful.
| // encode the text | ||
| val encoded = huffmanTree.encode(sourceText) | ||
| println("Encoded String: " + encoded) | ||
| println("Decoded String: " + huffmanTree.decode(encoded)) |
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For here and above, prefer template syntax rather than concatenation:
Suggested change
| println("Decoded String: " + huffmanTree.decode(encoded)) | |
| println("Decoded String: ${huffmanTree.decode(encoded)}") |
| } | ||
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| // recursively populate a codebook with encodings from a node | ||
| fun populateCodebook(node: Node, code: String, codebook: MutableMap<Char, String>) { |
| fun encode(letter: Char) = codebook[letter] | ||
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| // the reverse codebook is just the original one with keys as values and values as keys | ||
| val reverseCodebook: HashMap<String, Char> by lazy { |
| for (m in codebook.entries) { | ||
| reversed.put(m.value, m.key) | ||
| } | ||
| reversed |
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You can replace the whole block with
codebook.entries.associateBy({ it.value }) { it.key }| } | ||
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| // encode a string using the tree | ||
| fun encode(source: String): String { |
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Suggested change
| fun encode(source: String): String { | |
| fun encode(source: String) = source.map { codeBook.encode(it) }.joinToString(separator = "") |
replaces the whole function.
| val frequencyMap = HashMap<Char, Int>() | ||
| for (char in textSample) { | ||
| val newFrequency = (frequencyMap.get(char) ?: 0) + 1 | ||
| frequencyMap.put(char, newFrequency) |
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Replace both lines with
frequencyMap[char] = frequencyMap.getOrDefault(char, 0)| } | ||
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| // decode an encoded string | ||
| fun decode(encoded: String) = buildString { |
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I won't work it out for you, but some of this can be re-written using functional idioms.
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[lang: kotlin] |
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