139 lines
3.5 KiB
Dart
139 lines
3.5 KiB
Dart
/**
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* File: hash_map_chaining.dart
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* Created Time: 2023-06-24
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* Author: liuyuxin (gvenusleo@gmail.com)
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*/
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import 'array_hash_map.dart';
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/* Chained address hash table */
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class HashMapChaining {
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late int size; // Number of key-value pairs
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late int capacity; // Hash table capacity
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late double loadThres; // Load factor threshold for triggering expansion
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late int extendRatio; // Expansion multiplier
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late List<List<Pair>> buckets; // Bucket array
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/* Constructor */
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HashMapChaining() {
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size = 0;
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capacity = 4;
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loadThres = 2.0 / 3.0;
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extendRatio = 2;
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buckets = List.generate(capacity, (_) => []);
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}
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/* Hash function */
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int hashFunc(int key) {
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return key % capacity;
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}
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/* Load factor */
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double loadFactor() {
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return size / capacity;
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}
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/* Query operation */
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String? get(int key) {
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int index = hashFunc(key);
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List<Pair> bucket = buckets[index];
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// Traverse the bucket, if the key is found, return the corresponding val
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for (Pair pair in bucket) {
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if (pair.key == key) {
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return pair.val;
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}
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}
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// If key is not found, return null
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return null;
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}
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/* Add operation */
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void put(int key, String val) {
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// When the load factor exceeds the threshold, perform expansion
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if (loadFactor() > loadThres) {
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extend();
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}
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int index = hashFunc(key);
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List<Pair> bucket = buckets[index];
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// Traverse the bucket, if the specified key is encountered, update the corresponding val and return
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for (Pair pair in bucket) {
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if (pair.key == key) {
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pair.val = val;
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return;
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}
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}
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// If the key is not found, add the key-value pair to the end
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Pair pair = Pair(key, val);
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bucket.add(pair);
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size++;
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}
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/* Remove operation */
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void remove(int key) {
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int index = hashFunc(key);
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List<Pair> bucket = buckets[index];
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// Traverse the bucket, remove the key-value pair from it
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for (Pair pair in bucket) {
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if (pair.key == key) {
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bucket.remove(pair);
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size--;
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break;
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}
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}
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}
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/* Extend hash table */
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void extend() {
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// Temporarily store the original hash table
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List<List<Pair>> bucketsTmp = buckets;
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// Initialize the extended new hash table
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capacity *= extendRatio;
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buckets = List.generate(capacity, (_) => []);
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size = 0;
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// Move key-value pairs from the original hash table to the new hash table
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for (List<Pair> bucket in bucketsTmp) {
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for (Pair pair in bucket) {
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put(pair.key, pair.val);
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}
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}
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}
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/* Print hash table */
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void printHashMap() {
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for (List<Pair> bucket in buckets) {
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List<String> res = [];
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for (Pair pair in bucket) {
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res.add("${pair.key} -> ${pair.val}");
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}
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print(res);
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}
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}
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}
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/* Driver Code */
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void main() {
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/* Initialize hash table */
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HashMapChaining map = HashMapChaining();
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/* Add operation */
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// Add key-value pair (key, value) to the hash table
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map.put(12836, "Ha");
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map.put(15937, "Luo");
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map.put(16750, "Suan");
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map.put(13276, "Fa");
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map.put(10583, "Ya");
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print("\nAfter adding, the hash table is\nKey -> Value");
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map.printHashMap();
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/* Query operation */
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// Enter key to the hash table, get value
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String? name = map.get(13276);
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print("\nInput student ID 13276, found name ${name}");
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/* Remove operation */
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// Remove key-value pair (key, value) from the hash table
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map.remove(12836);
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print("\nAfter removing 12836, the hash table is\nKey -> Value");
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map.printHashMap();
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}
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