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krahets
2023-09-24 16:54:10 +08:00
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261
chapter_hashing/hash_collision.md
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@@ -1741,21 +1741,17 @@ comments: true
```csharp title="hash_map_open_addressing.cs"
/* 开放寻址哈希表 */
class HashMapOpenAddressing {
int size; // 键值对数量
int capacity; // 哈希表容量
double loadThres; // 触发扩容的负载因子阈值
int extendRatio; // 扩容倍数
Pair[] buckets; // 桶数组
Pair removed; // 删除标记
private int size; // 键值对数量
private int capacity = 4; // 哈希表容量
private double loadThres = 2.0 / 3; // 触发扩容的负载因子阈值
private int extendRatio = 2; // 扩容倍数
private Pair[] buckets; // 桶数组
private Pair TOMBSTONE = new Pair(-1, "-1"); // 删除标记
/* 构造方法 */
public HashMapOpenAddressing() {
size = 0;
capacity = 4;
loadThres = 2.0 / 3.0;
extendRatio = 2;
buckets = new Pair[capacity];
removed = new Pair(-1, "-1");
}
/* 哈希函数 */
@@ -1768,20 +1764,42 @@ comments: true
return (double)size / capacity;
}
/* 搜索 key 对应的桶索引 */
private int findBucket(int key) {
int index = hashFunc(key);
int firstTombstone = -1;
// 线性探测，当遇到空桶时跳出
while (buckets[index] != null) {
// 若遇到 key ，返回对应桶索引
if (buckets[index].key == key) {
// 若之前遇到了删除标记，则将键值对移动至该索引
if (firstTombstone != -1) {
buckets[firstTombstone] = buckets[index];
buckets[index] = TOMBSTONE;
return firstTombstone; // 返回移动后的桶索引
}
return index; // 返回桶索引
}
// 记录遇到的首个删除标记
if (firstTombstone == -1 && buckets[index] == TOMBSTONE) {
firstTombstone = index;
}
// 计算桶索引，越过尾部返回头部
index = (index + 1) % capacity;
}
// 若 key 不存在，则返回添加点的索引
return firstTombstone == -1 ? index : firstTombstone;
}
/* 查询操作 */
public string get(int key) {
int index = hashFunc(key);
// 线性探测，从 index 开始向后遍历
for (int i = 0; i < capacity; i++) {
// 计算桶索引，越过尾部返回头部
int j = (index + i) % capacity;
// 若遇到空桶，说明无此 key ，则返回 null
if (buckets[j] == null)
return null;
// 若遇到指定 key ，则返回对应 val
if (buckets[j].key == key && buckets[j] != removed)
return buckets[j].val;
// 搜索 key 对应的桶索引
int index = findBucket(key);
// 若找到键值对，则返回对应 val
if (buckets[index] != null && buckets[index] != TOMBSTONE) {
return buckets[index].val;
}
// 若键值对不存在，则返回 null
return null;
}
@@ -1791,42 +1809,26 @@ comments: true
if (loadFactor() > loadThres) {
extend();
}
int index = hashFunc(key);
// 线性探测，从 index 开始向后遍历
for (int i = 0; i < capacity; i++) {
// 计算桶索引，越过尾部返回头部
int j = (index + i) % capacity;
// 若遇到空桶、或带有删除标记的桶，则将键值对放入该桶
if (buckets[j] == null || buckets[j] == removed) {
buckets[j] = new Pair(key, val);
size += 1;
return;
}
// 若遇到指定 key ，则更新对应 val
if (buckets[j].key == key) {
buckets[j].val = val;
return;
}
// 搜索 key 对应的桶索引
int index = findBucket(key);
// 若找到键值对，则覆盖 val 并返回
if (buckets[index] != null && buckets[index] != TOMBSTONE) {
buckets[index].val = val;
return;
}
// 若键值对不存在，则添加该键值对
buckets[index] = new Pair(key, val);
size++;
}
/* 删除操作 */
public void remove(int key) {
int index = hashFunc(key);
// 线性探测，从 index 开始向后遍历
for (int i = 0; i < capacity; i++) {
// 计算桶索引，越过尾部返回头部
int j = (index + i) % capacity;
// 若遇到空桶，说明无此 key ，则直接返回
if (buckets[j] == null) {
return;
}
// 若遇到指定 key ，则标记删除并返回
if (buckets[j].key == key) {
buckets[j] = removed;
size -= 1;
return;
}
// 搜索 key 对应的桶索引
int index = findBucket(key);
// 若找到键值对，则用删除标记覆盖它
if (buckets[index] != null && buckets[index] != TOMBSTONE) {
buckets[index] = TOMBSTONE;
size--;
}
}
@@ -1840,7 +1842,7 @@ comments: true
size = 0;
// 将键值对从原哈希表搬运至新哈希表
foreach (Pair pair in bucketsTmp) {
if (pair != null && pair != removed) {
if (pair != null && pair != TOMBSTONE) {
put(pair.key, pair.val);
}
}
@@ -1849,10 +1851,12 @@ comments: true
/* 打印哈希表 */
public void print() {
foreach (Pair pair in buckets) {
if (pair != null) {
Console.WriteLine(pair.key + " -> " + pair.val);
} else {
if (pair == null) {
Console.WriteLine("null");
} else if (pair == TOMBSTONE) {
Console.WriteLine("TOMBSTONE");
} else {
Console.WriteLine(pair.key + " -> " + pair.val);
}
}
}
@@ -2503,12 +2507,12 @@ comments: true
```rust title="hash_map_open_addressing.rs"
/* 开放寻址哈希表 */
struct HashMapOpenAddressing {
size: usize,
capacity: usize,
load_thres: f32,
extend_ratio: usize,
buckets: Vec<Option<Pair>>,
removed: Pair,
size: usize, // 键值对数量
capacity: usize, // 哈希表容量
load_thres: f64, // 触发扩容的负载因子阈值
extend_ratio: usize, // 扩容倍数
buckets: Vec<Option<Pair>>, // 桶数组
TOMBSTONE: Option<Pair>, // 删除标记
}
@@ -2521,10 +2525,7 @@ comments: true
load_thres: 2.0 / 3.0,
extend_ratio: 2,
buckets: vec![None; 4],
removed: Pair {
key: -1,
val: "-1".to_string(),
},
TOMBSTONE: Some(Pair {key: -1, val: "-1".to_string()}),
}
}
@@ -2534,27 +2535,46 @@ comments: true
}
/* 负载因子 */
fn load_factor(&self) -> f32 {
self.size as f32 / self.capacity as f32
fn load_factor(&self) -> f64 {
self.size as f64 / self.capacity as f64
}
/* 搜索 key 对应的桶索引 */
fn find_bucket(&mut self, key: i32) -> usize {
let mut index = self.hash_func(key);
let mut first_tombstone = -1;
// 线性探测，当遇到空桶时跳出
while self.buckets[index].is_some() {
// 若遇到 key，返回对应的桶索引
if self.buckets[index].as_ref().unwrap().key == key {
// 若之前遇到了删除标记，则将建值对移动至该索引
if first_tombstone != -1 {
self.buckets[first_tombstone as usize] = self.buckets[index].take();
self.buckets[index] = self.TOMBSTONE.clone();
return first_tombstone as usize; // 返回移动后的桶索引
}
return index; // 返回桶索引
}
// 记录遇到的首个删除标记
if first_tombstone == -1 && self.buckets[index] == self.TOMBSTONE {
first_tombstone = index as i32;
}
// 计算桶索引，越过尾部返回头部
index = (index + 1) % self.capacity;
}
// 若 key 不存在，则返回添加点的索引
if first_tombstone == -1 { index } else { first_tombstone as usize }
}
/* 查询操作 */
fn get(&self, key: i32) -> Option<&str> {
let mut index = self.hash_func(key);
let capacity = self.capacity;
// 线性探测，从 index 开始向后遍历
for _ in 0..capacity {
// 计算桶索引，越过尾部返回头部
let j = (index + 1) % capacity;
match &self.buckets[j] {
// 若遇到空桶，说明无此 key ，则返回 None
None => return None,
// 若遇到指定 key ，则返回对应 val
Some(pair) if pair.key == key && pair != &self.removed => return Some(&pair.val),
_ => index = j,
}
fn get(&mut self, key: i32) -> Option<&str> {
// 搜索 key 对应的桶索引
let index = self.find_bucket(key);
// 若找到键值对，则返回对应 val
if self.buckets[index].is_some() && self.buckets[index] != self.TOMBSTONE {
return self.buckets[index].as_ref().map(|pair| &pair.val as &str);
}
// 若键值对不存在，则返回 null
None
}
@@ -2564,57 +2584,29 @@ comments: true
if self.load_factor() > self.load_thres {
self.extend();
}
let mut index = self.hash_func(key);
let capacity = self.capacity;
// 线性探测，从 index 开始向后遍历
for _ in 0..capacity {
//计算桶索引，越过尾部返回头部
let j = (index + 1) % capacity;
// 若遇到空桶、或带有删除标记的桶，则将键值对放入该桶
match &mut self.buckets[j] {
bucket @ &mut None | bucket @ &mut Some(Pair { key: -1, .. }) => {
*bucket = Some(Pair { key, val });
self.size += 1;
return;
}
// 若遇到指定 key ，则更新对应 val
Some(pair) if pair.key == key => {
pair.val = val;
return;
}
_ => index = j,
}
// 搜索 key 对应的桶索引
let index = self.find_bucket(key);
// 若找到键值对，则覆盖 val 并返回
if self.buckets[index].is_some() && self.buckets[index] != self.TOMBSTONE {
self.buckets[index].as_mut().unwrap().val = val;
return;
}
// 若键值对不存在，则添加该键值对
self.buckets[index] = Some(Pair { key, val });
self.size += 1;
}
/* 删除操作 */
fn remove(&mut self, key: i32) {
let mut index = self.hash_func(key);
let capacity = self.capacity;
// 遍历桶，从中删除键值对
for _ in 0..capacity {
let j = (index + 1) % capacity;
match &mut self.buckets[j] {
// 若遇到空桶，说明无此 key ，则直接返回
None => return,
// 若遇到指定 key ，则标记删除并返回
Some(pair) if pair.key == key => {
*pair = Pair {
key: -1,
val: "-1".to_string(),
};
self.size -= 1;
return;
}
_ => index = j,
}
// 搜索 key 对应的桶索引
let index = self.find_bucket(key);
// 若找到键值对，则用删除标记覆盖它
if self.buckets[index].is_some() && self.buckets[index] != self.TOMBSTONE {
self.buckets[index] = self.TOMBSTONE.clone();
self.size -= 1;
}
}
/* 扩容哈希表 */
fn extend(&mut self) {
// 暂存原哈希表
@@ -2626,17 +2618,24 @@ comments: true
// 将键值对从原哈希表搬运至新哈希表
for pair in buckets_tmp {
if let Some(pair) = pair {
self.put(pair.key, pair.val);
if pair.is_none() || pair == self.TOMBSTONE {
continue;
}
let pair = pair.unwrap();
self.put(pair.key, pair.val);
}
}
/* 打印哈希表 */
fn print(&self) {
for pair in &self.buckets {
match pair {
Some(pair) => println!("{} -> {}", pair.key, pair.val),
None => println!("None"),
if pair.is_none() {
println!("null");
} else if pair == &self.TOMBSTONE {
println!("TOMBSTONE");
} else {
let pair = pair.as_ref().unwrap();
println!("{} -> {}", pair.key, pair.val);
}
}
}

1
chapter_hashing/hash_map.md
View File

@@ -1329,6 +1329,7 @@ index = hash(key) % capacity
```rust title="array_hash_map.rs"
/* 键值对 */
#[derive(Debug, Clone, PartialEq)]
pub struct Pair {
pub key: i32,
pub val: String,