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B树也称B-树#xff0c;注意不是减号#xff0c;是一棵多路平衡查找树#xff1b;理论上#xff0c;二叉搜索树 #xff08;BST#xff09; 是最佳的选择排序映射#xff0c;但是每次查找时层数越多I/O次数越多#xff0c;B 树使每个节…std::collections::BTreeMap定义
B树也称B-树注意不是减号是一棵多路平衡查找树理论上二叉搜索树 BST 是最佳的选择排序映射但是每次查找时层数越多I/O次数越多B 树使每个节点都包含连续数组中的 B-1 到 2B-1 元素可以减少树的高度减少I/O次数
BTreeMap定义
pub struct BTreeMapK, V, A: Allocator Clone Global {// B 树的根节点root: OptionRootK, V,// B 树映射中存储的键值对的数量length: usize,// 分配器pub(super) alloc: ManuallyDropA,// PhantomData是一个零大小的类型用于向编译器提供类型信息但在运行时不占用任何空间_marker: PhantomDatacrate::boxed::Box(K, V), A,
}方法
clear用于清空BTreeMap移除所有的键值对
use std::collections::BTreeMap;fn main() {let mut map BTreeMap::new();map.insert(a, 1);map.insert(b, 2);map.clear();println!(After clear, is empty? {}, map.is_empty());// After clear, is empty? true
}get用于获取指定键对应的值的不可变引用如果键不存在则返回None
use std::collections::BTreeMap;fn main() {let map BTreeMap::from([(a, 1),(b, 2),]);if let Some(value) map.get(a) {println!(Value for a: {}, value);// Value for a: 1} else {println!(a not found.);}
}get_key_value返回指定键对应的值和键的不可变引用如果键不存在则返回None
use std::collections::BTreeMap;fn main() {let map BTreeMap::from([(a, 1),(b, 2),]);if let Some((key, value)) map.get_key_value(b) {println!(Key-value pair for b: {} - {}, key, value);// Key-value pair for b: b - 2} else {println!(b not found.);}
}first_key_value返回BTreeMap中的第一个键值对如果地图为空则返回None
use std::collections::BTreeMap;fn main() {let map BTreeMap::from([(a, 1),(b, 2),]);if let Some((first_key, first_value)) map.first_key_value() {println!(First key-value pair: {} - {}, first_key, first_value);// First key-value pair: a - 1} else {println!(Map is empty.);}
}first_entry返回一个可变引用到BTreeMap中的第一个键值对如果地图为空则返回None
use std::collections::BTreeMap;fn main() {let mut map BTreeMap::from([(a, 1),(b, 2),]);if let Some(first_entry) map.first_entry() {println!(First entry: {} - {}, first_entry.key(), first_entry.get());// First entry: a - 1} else {println!(Map is empty.);}
}pop_first移除并返回BTreeMap中的第一个键值对如果地图为空则返回None
use std::collections::BTreeMap;fn main() {let mut map BTreeMap::from([(a, 1),(b, 2),]);if let Some((popped_key, popped_value)) map.pop_first() {println!(Popped first pair: {} - {}, popped_key, popped_value);// Popped first pair: a - 1} else {println!(Map is empty.);}
}pop_last移除并返回BTreeMap中的最后一个键值对如果地图为空则返回None
use std::collections::BTreeMap;fn main() {let mut map BTreeMap::from([(a, 1),(b, 2),]);if let Some((last_key, last_value)) map.pop_last() {println!(Popped last pair: {} - {}, last_key, last_value);// Popped last pair: b - 2} else {println!(Map is empty.);}
}contains_key判断BTreeMap中是否存在指定的键
use std::collections::BTreeMap;fn main() {let map BTreeMap::from([(a, 1),(b, 2),]);println!(Contains a? {}, map.contains_key(a));// Contains a? true
}get_mut返回指定键对应的值的可变引用如果键不存在则返回None
use std::collections::BTreeMap;fn main() {let mut map BTreeMap::from([(a, 1),(b, 2),]);if let Some(value) map.get_mut(a) {*value 3;println!(Modified value for a: {}, value);// Modified value for a: 3} else {println!(a not found.);}
}insert插入一个键值对到BTreeMap中如果键已经存在则覆盖旧值
use std::collections::BTreeMap;fn main() {let mut map BTreeMap::new();map.insert(a, 1);map.insert(a, 2);println!(After insert: {:?}, map);// After insert: {a: 2}
}remove移除指定键对应的键值对并返回被移除的值如果键不存在则返回None
use std::collections::BTreeMap;fn main() {let mut map BTreeMap::from([(a, 1),(b, 2),]);if let Some(removed_value) map.remove(a) {println!(Removed value for a: {}, removed_value);// Removed value for a: 1} else {println!(a not found.);}
}remove_entry移除指定键对应的键值对并返回被移除的键值对如果键不存在则返回None
use std::collections::BTreeMap;fn main() {let mut map BTreeMap::from([(a, 1),(b, 2),]);if let Some((removed_key, removed_value)) map.remove_entry(b) {println!(Removed entry: {} - {}, removed_key, removed_value);// Removed entry: b - 2} else {println!(b not found.);}
}retain保留满足给定谓词的键值对
use std::collections::BTreeMap;fn main() {let mut map BTreeMap::from([(a, 1),(b, 2),(c, 3),]);map.retain(|key, value| (*key b || *value 2));println!(After retain: {:?}, map);// After retain: {b: 2, c: 3}
}append将另一个BTreeMap的键值对追加到当前BTreeMap中
use std::collections::BTreeMap;fn main() {let mut map1 BTreeMap::from([(a, 1),(b, 2),]);let mut map2 BTreeMap::from([(c, 3),(d, 4),]);map1.append(mut map2);println!(After append: {:?}, map1);// After append: {a: 1, b: 2, c: 3, d: 4}
}range返回一个迭代器遍历BTreeMap中满足给定范围条件的键值对
use std::collections::BTreeMap;fn main() {let map BTreeMap::from([(a, 1),(b, 2),(c, 3),(d, 4),]);for (key, value) in map.range(b..) {println!(In range: {} - {}, key, value);}// In range: b - 2// In range: c - 3// In range: d - 4
}range_mut返回一个可变迭代器遍历BTreeMap中满足给定范围条件的键值对并允许修改值
use std::collections::BTreeMap;fn main() {let mut map BTreeMap::from([(a, 1),(b, 2),(c, 3),(d, 4),]);for (key, value) in map.range_mut(b..) {*value *value * 2;println!(Modified in range: {} - {}, key, value);}// Modified in range: b - 4// Modified in range: c - 6// Modified in range: d - 8
}entry返回一个Entry API可以用于插入或更新键值对
use std::collections::BTreeMap;fn main() {let mut map BTreeMap::new();let entry map.entry(a).or_insert(1);println!(Entry value for a: {}, entry);// Entry value for a: 1
}split_off移除并返回给定键及其对应的值如果键不存在则返回None和一个空BTreeMap into_keys将BTreeMap的键提取为一个可迭代的集合
use std::collections::BTreeMap;fn main() {let map BTreeMap::from([(a, 1),(b, 2),]);let keys: Vec_ map.into_keys().collect();println!(Keys: {:?}, keys);// Keys: [a, b]
}into_values将BTreeMap的值提取为一个可迭代的集合
use std::collections::BTreeMap;fn main() {let map BTreeMap::from([(a, 1),(b, 2),]);let values: Vec_ map.into_values().collect();println!(Values: {:?}, values);// Values: [1, 2]
}iter返回一个迭代器遍历BTreeMap的键值对
use std::collections::BTreeMap;fn main() {let map BTreeMap::from([(a, 1),(b, 2),]);for (key, value) in map.iter() {println!(Iter: {} - {}, key, value);}// Iter: a - 1// Iter: b - 2
}iter_mut返回一个可变迭代器允许修改BTreeMap的键值对
use std::collections::BTreeMap;fn main() {let mut map BTreeMap::from([(a, 1),(b, 2),]);for (key, value) in map.iter_mut() {*value *value * 2;println!(Mut iter: {} - {}, key, value);}// Mut iter: a - 2// Mut iter: b - 4
}keys返回一个迭代器遍历BTreeMap的键
use std::collections::BTreeMap;fn main() {let map BTreeMap::from([(a, 1),(b, 2),]);for key in map.keys() {println!(Key from keys: {}, key);}// Key from keys: a// Key from keys: b
}values返回一个迭代器遍历BTreeMap的值
use std::collections::BTreeMap;fn main() {let map BTreeMap::from([(a, 1),(b, 2),]);for value in map.values() {println!(Value from values: {}, value);}// Value from values: 1// Value from values: 2
}values_mut返回一个可变迭代器允许修改BTreeMap的值
use std::collections::BTreeMap;fn main() {let mut map BTreeMap::from([(a, 1),(b, 2),]);for value in map.values_mut() {*value *value * 3;println!(Mut value from values_mut: {}, value);}// Mut value from values_mut: 3// Mut value from values_mut: 6
}len返回BTreeMap中键值对的数量
use std::collections::BTreeMap;fn main() {let map BTreeMap::from([(a, 1),(b, 2),]);println!(Length: {}, map.len());// Length: 2
}is_empty判断BTreeMap是否为空
use std::collections::BTreeMap;fn main() {let map: BTreeMapi32, str BTreeMap::new();println!(Is empty: {}, map.is_empty());// Is empty: true
}
