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https://github.com/krahets/hello-algo.git
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56b20eff36
* .net 8.0 migration * update docs * revert change * revert change and update appendix docs * remove static * Update binary_search_insertion.cs * Update binary_search_insertion.cs * Update binary_search_edge.cs * Update binary_search_insertion.cs * Update binary_search_edge.cs --------- Co-authored-by: Yudong Jin <krahets@163.com>
159 lines
4.9 KiB
C#
159 lines
4.9 KiB
C#
/**
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* File: hash_map_open_addressing.cs
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* Created Time: 2023-06-26
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* Author: hpstory (hpstory1024@163.com)
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*/
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namespace hello_algo.chapter_hashing;
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/* 开放寻址哈希表 */
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class HashMapOpenAddressing {
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int size; // 键值对数量
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int capacity = 4; // 哈希表容量
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double loadThres = 2.0 / 3.0; // 触发扩容的负载因子阈值
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int extendRatio = 2; // 扩容倍数
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Pair[] buckets; // 桶数组
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Pair TOMBSTONE = new(-1, "-1"); // 删除标记
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/* 构造方法 */
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public HashMapOpenAddressing() {
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size = 0;
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buckets = new Pair[capacity];
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}
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/* 哈希函数 */
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int HashFunc(int key) {
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return key % capacity;
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}
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/* 负载因子 */
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double LoadFactor() {
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return (double)size / capacity;
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}
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/* 搜索 key 对应的桶索引 */
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int FindBucket(int key) {
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int index = HashFunc(key);
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int firstTombstone = -1;
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// 线性探测,当遇到空桶时跳出
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while (buckets[index] != null) {
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// 若遇到 key ,返回对应桶索引
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if (buckets[index].key == key) {
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// 若之前遇到了删除标记,则将键值对移动至该索引
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if (firstTombstone != -1) {
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buckets[firstTombstone] = buckets[index];
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buckets[index] = TOMBSTONE;
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return firstTombstone; // 返回移动后的桶索引
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}
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return index; // 返回桶索引
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}
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// 记录遇到的首个删除标记
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if (firstTombstone == -1 && buckets[index] == TOMBSTONE) {
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firstTombstone = index;
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}
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// 计算桶索引,越过尾部返回头部
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index = (index + 1) % capacity;
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}
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// 若 key 不存在,则返回添加点的索引
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return firstTombstone == -1 ? index : firstTombstone;
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}
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/* 查询操作 */
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public string? Get(int key) {
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// 搜索 key 对应的桶索引
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int index = FindBucket(key);
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// 若找到键值对,则返回对应 val
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if (buckets[index] != null && buckets[index] != TOMBSTONE) {
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return buckets[index].val;
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}
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// 若键值对不存在,则返回 null
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return null;
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}
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/* 添加操作 */
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public void Put(int key, string val) {
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// 当负载因子超过阈值时,执行扩容
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if (LoadFactor() > loadThres) {
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Extend();
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}
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// 搜索 key 对应的桶索引
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int index = FindBucket(key);
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// 若找到键值对,则覆盖 val 并返回
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if (buckets[index] != null && buckets[index] != TOMBSTONE) {
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buckets[index].val = val;
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return;
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}
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// 若键值对不存在,则添加该键值对
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buckets[index] = new Pair(key, val);
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size++;
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}
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/* 删除操作 */
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public void Remove(int key) {
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// 搜索 key 对应的桶索引
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int index = FindBucket(key);
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// 若找到键值对,则用删除标记覆盖它
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if (buckets[index] != null && buckets[index] != TOMBSTONE) {
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buckets[index] = TOMBSTONE;
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size--;
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}
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}
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/* 扩容哈希表 */
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void Extend() {
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// 暂存原哈希表
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Pair[] bucketsTmp = buckets;
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// 初始化扩容后的新哈希表
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capacity *= extendRatio;
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buckets = new Pair[capacity];
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size = 0;
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// 将键值对从原哈希表搬运至新哈希表
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foreach (Pair pair in bucketsTmp) {
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if (pair != null && pair != TOMBSTONE) {
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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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/* 打印哈希表 */
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public void Print() {
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foreach (Pair pair in buckets) {
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if (pair == null) {
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Console.WriteLine("null");
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} else if (pair == TOMBSTONE) {
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Console.WriteLine("TOMBSTONE");
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} else {
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Console.WriteLine(pair.key + " -> " + pair.val);
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}
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}
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}
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}
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public class hash_map_open_addressing {
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[Test]
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public void Test() {
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/* 初始化哈希表 */
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HashMapOpenAddressing map = new();
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/* 添加操作 */
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// 在哈希表中添加键值对 (key, value)
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map.Put(12836, "小哈");
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map.Put(15937, "小啰");
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map.Put(16750, "小算");
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map.Put(13276, "小法");
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map.Put(10583, "小鸭");
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Console.WriteLine("\n添加完成后,哈希表为\nKey -> Value");
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map.Print();
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/* 查询操作 */
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// 向哈希表输入键 key ,得到值 value
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string? name = map.Get(13276);
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Console.WriteLine("\n输入学号 13276 ,查询到姓名 " + name);
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/* 删除操作 */
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// 在哈希表中删除键值对 (key, value)
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map.Remove(16750);
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Console.WriteLine("\n删除 16750 后,哈希表为\nKey -> Value");
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map.Print();
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}
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}
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