阿里云服务器搭建wordpress,惠州seo排名收费,福州学做网站,家居网站建设的需求分析文章目录 一、Map类型1.HashMaphashMap的简单插入entry().or_insert()更新hashMap 2.什么时候用HashMap3.HashMap中的键 二、BTreeMap1.什么时候用BTreeMap2.BTreeMap中的键 参考 一、Map类型
键值对数据又称字典数据类型
主要有两种 HashMap - BTreeMap
1.HashMap
HashM… 文章目录 一、Map类型1.HashMaphashMap的简单插入entry().or_insert()更新hashMap 2.什么时候用HashMap3.HashMap中的键 二、BTreeMap1.什么时候用BTreeMap2.BTreeMap中的键 参考 一、Map类型
·键值对数据又称字典数据类型
·主要有两种
· HashMap ·- BTreeMap
1.HashMap
·HashMapK,V类型储存了一个键类型K对应一个值类型V的映射。它通过一个 哈希函数hashing function来实现映射决定如何将键和值放入内存中。
·HashMap的数据和Vec一样在heap上
hashMap的简单插入
#![allow(unused)]
fn main() {use std::collections::HashMap;let mut scores HashMap::new();scores.insert(String::from(Blue), 10);scores.insert(String::from(Yellow), 50);for (key, value) in scores {println!({}: {}, key, value);}
}
cargo runCompiling abc v0.1.0 (/home/wangji/installer/rust/bobo/abc)Finished dev profile [unoptimized debuginfo] target(s) in 0.91sRunning target/debug/abc
Yellow: 50
Blue: 10entry().or_insert()更新hashMap
直接覆盖 #![allow(unused)]
fn main() {
use std::collections::HashMap;let mut scores HashMap::new();scores.insert(String::from(Blue), 10);
scores.insert(String::from(Blue), 25);println!({:?}, scores);
}or_insert在没有key的情况下才插入
#![allow(unused)]
fn main() {use std::collections::HashMap;let mut scores HashMap::new();scores.insert(String::from(Blue), 10);scores.entry(String::from(Yellow)).or_insert(50);scores.entry(String::from(Blue)).or_insert(50);println!({:?}, scores);
}
cargo runBlocking waiting for file lock on package cacheBlocking waiting for file lock on package cacheCompiling abc v0.1.0 (/home/wangji/installer/rust/bobo/abc)Finished dev profile [unoptimized debuginfo] target(s) in 13.96sRunning target/debug/abc
{Blue: 10, Yellow: 50}or_inser根据旧值更新一个值会返回插入的pair的value的引用
#![allow(unused)]
fn main() {use std::collections::HashMap;let text hello world wonderful world;let mut map HashMap::new();for word in text.split_whitespace() {let count map.entry(word).or_insert(0);*count 1;}println!({:?}, map);
}
cargo runFinished dev profile [unoptimized debuginfo] target(s) in 0.00sRunning target/debug/abc
{hello: 1, wonderful: 1, world: 2}2.什么时候用HashMap
·仅次于Vec的常用数据类型 ·存储数据为键值对类型 需要查找的速度
in-memory cache
3.HashMap中的键
·因为要满足哈希函数所以HashMap对键有特殊要求 ·实现Hash、Eq、PartialEq ·一般结构体 #[derive(Debug, PartialEq, Hash, Eq)]
use std::collections::HashMap;// Hash Eq PartialEq
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
struct Car {id: i32,price: i32,
}fn main() {let _int_map: HashMapi32, i32 HashMap::new();let _int_map: HashMapi32, i32 HashMap::with_capacity(10);// 通过数组来创建maplet mut car_map HashMap::from([(Car1,Car {id: 1,price: 10000,},),(Car2, Car { id: 2, price: 4000 }),(Car3,Car {id: 3,price: 890000,},),]);// 打印实际是无序的for (k, v) in car_map {println!({k}:{:?}, v);}// getprintln!(Some {:?}, car_map.get(Car1));println!(None {:?}, car_map.get(Car6));// 覆盖性插入insertcar_map.insert(Car4,Car {id: 4,price: 80000,},);println!({:?}, car_map);car_map.insert(Car4,Car {id: 5,price: 300000,},);println!({:?}, car_map);// 只在键没有时插入// Entrycar_map.entry(Car4).or_insert(Car { id: 9, price: 9000 });println!({:?}, car_map);// removecar_map.remove(Car4);println!({:?}, car_map);car_map.entry(Car4).or_insert(Car { id: 9, price: 9000 });println!({:?}, car_map);// 加上注释PartialEq, Eq, Hashlet mut car_map HashMap::from([(Car {id: 1,price: 10000,},Car1,),(Car { id: 2, price: 4000 }, Car2),(Car {id: 3,price: 890000,},Car3,),]);println!(Car2: {:?}\n,car_map.get(Car {id: 1,price: 10000}));for (car, name) in car_map {println!({:?}: {name}, car)}// Filter会原地修改mapcar_map.retain(|c, _| c.price 5000);println!( 4000 {:?}, car_map);
}
编译及运行
cargo runBlocking waiting for file lock on build directoryCompiling data_struct v0.1.0 (/home/wangji/installer/rust/data_struct/data_struct)Finished dev profile [unoptimized debuginfo] target(s) in 13.52sRunning target/debug/data_struct
Car1:Car { id: 1, price: 10000 }
Car3:Car { id: 3, price: 890000 }
Car2:Car { id: 2, price: 4000 }
Some Some(Car { id: 1, price: 10000 })
None None
{Car4: Car { id: 4, price: 80000 }, Car2: Car { id: 2, price: 4000 }, Car1: Car { id: 1, price: 10000 }, Car3: Car { id: 3, price: 890000 }}
{Car4: Car { id: 5, price: 300000 }, Car2: Car { id: 2, price: 4000 }, Car1: Car { id: 1, price: 10000 }, Car3: Car { id: 3, price: 890000 }}
{Car4: Car { id: 5, price: 300000 }, Car2: Car { id: 2, price: 4000 }, Car1: Car { id: 1, price: 10000 }, Car3: Car { id: 3, price: 890000 }}
{Car2: Car { id: 2, price: 4000 }, Car1: Car { id: 1, price: 10000 }, Car3: Car { id: 3, price: 890000 }}
{Car4: Car { id: 9, price: 9000 }, Car2: Car { id: 2, price: 4000 }, Car1: Car { id: 1, price: 10000 }, Car3: Car { id: 3, price: 890000 }}
Car2: Some(Car1)Car { id: 3, price: 890000 }: Car3
Car { id: 1, price: 10000 }: Car1
Car { id: 2, price: 4000 }: Car24000 {Car { id: 2, price: 4000 }: Car2}二、BTreeMap
map的有序形式
内部基于BTree创建
1.什么时候用BTreeMap
·当你需要有序map时 ·当你查找时有序可以提供你的性能 (比如二分查找法) ·注意有序是有代价的 ·BTreeMap缓存效率和搜索中进行了折衷
2.BTreeMap中的键
·因为需要对键值排序所以需要Key实现
OrdPartialOrd
use std::collections::BTreeMap;// Hash Eq PartialEq
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
struct Car {id: i32,price: i32,
}impl Ord for Car {fn cmp(self, other: Self) - std::cmp::Ordering {self.price.cmp(other.price)}
}impl PartialOrd for Car {fn partial_cmp(self, other: Self) - Optionstd::cmp::Ordering {Some(self.price.cmp(other.price))}
}fn main() {let _int_map: BTreeMapi32, i32 BTreeMap::new();// let _int_map:BTreeMapi32, i32 BTreeMap::with_capacity(10);// 通过数组来创建maplet mut car_map BTreeMap::from([(Car1,Car {id: 1,price: 10000,},),(Car2, Car { id: 2, price: 4000 }),(Car3,Car {id: 3,price: 890000,},),]);println!({:#?}, car_map);println!(------------------------);let mut car_map BTreeMap::from([(Car {id: 1,price: 10000,},1,),(Car { id: 2, price: 4000 }, 2),(Car {id: 3,price: 890000,},3,),]);for (k, v) in car_map {println!({:?}: {v}, k);}println!(----------------------);car_map.insert(Car {id: 4,price: 90000,},4,);for (k, v) in car_map {println!({:?}: {v}, k);}println!(----------------------);println!({:?},car_map.get(Car {id: 1,price: 10000}));println!({:?}, car_map.first_key_value());println!({:?}, car_map.last_key_value());println!(----------------------);// removelet car car_map.pop_first().unwrap();println!({:?}, car);let car car_map.pop_last().unwrap();println!({:?}, car);println!(----------------------);for (k, v) in car_map {println!({:?}: {v}, k);}println!(----------------------);// remove(index)不建议你用car_map.remove(Car {id: 1,price: 10000,});for (k, v) in car_map {println!({:?}: {v}, k);}println!(----------------------);car_map.clear();println!({}, car_map.is_empty());
}
编译及运行
cargo runCompiling data_struct v0.1.0 (/home/wangji/installer/rust/data_struct/data_struct)
warning: variable does not need to be mutable-- src/main.rs:27:9|
27 | let mut car_map BTreeMap::from([| ----^^^^^^^| || help: remove this mut| note: #[warn(unused_mut)] on by defaultwarning: data_struct (bin data_struct) generated 1 warning (run cargo fix --bin data_struct to apply 1 suggestion)Finished dev profile [unoptimized debuginfo] target(s) in 6.51sRunning target/debug/data_struct
{Car1: Car {id: 1,price: 10000,},Car2: Car {id: 2,price: 4000,},Car3: Car {id: 3,price: 890000,},
}
------------------------
Car { id: 2, price: 4000 }: 2
Car { id: 1, price: 10000 }: 1
Car { id: 3, price: 890000 }: 3
----------------------
Car { id: 2, price: 4000 }: 2
Car { id: 1, price: 10000 }: 1
Car { id: 4, price: 90000 }: 4
Car { id: 3, price: 890000 }: 3
----------------------
Some(1)
Some((Car { id: 2, price: 4000 }, 2))
Some((Car { id: 3, price: 890000 }, 3))
----------------------
(Car { id: 2, price: 4000 }, 2)
(Car { id: 3, price: 890000 }, 3)
----------------------
Car { id: 1, price: 10000 }: 1
Car { id: 4, price: 90000 }: 4
----------------------
Car { id: 4, price: 90000 }: 4
----------------------
true参考
Rust常用数据结构教程
