在 Vec 的中间或开头有效地插入或替换多个元素? [英] Efficiently insert or replace multiple elements in the middle or at the beginning of a Vec?

问题描述

是否有任何直接的方法可以插入或替换来自 &[T] 和/或 Vec 中的多个元素?Vec 在线性时间内?

Is there any straightforward way to insert or replace multiple elements from &[T] and/or Vec<T> in the middle or at the beginning of a Vec in linear time?

我只能找到 std::vec::Vec::insert，但这只是为了在 O(n) 时间内插入单个元素，所以我显然不能在循环中调用它.

I could only find std::vec::Vec::insert, but that's only for inserting a single element in O(n) time, so I obviously cannot call that in a loop.

我可以在那个索引处做一个split_off，extend新元素到分裂的左半部分，然后 将后半部分扩展到前半部分，但有更好的方法吗?

I could do a split_off at that index, extend the new elements into the left half of the split, and then extend the second half into the first, but is there a better way?

推荐答案

从 Rust 1.21.0 开始，Vec::splice 可用并允许在任何点插入，包括完全前置:

As of Rust 1.21.0, Vec::splice is available and allows inserting at any point, including fully prepending:

let mut vec = vec![1, 5];
let slice = &[2, 3, 4];

vec.splice(1..1, slice.iter().cloned());

println!("{:?}", vec); // [1, 2, 3, 4, 5]

文档状态:

注意 4:这是最佳选择:

Note 4: This is optimal if:

• 尾部(范围后向量中的元素)为空
• 或 replace_with 产生的元素少于范围的长度
• 或其 size_hint() 的下限是精确的.

• The tail (elements in the vector after range) is empty
• or replace_with yields fewer elements than range’s length
• or the lower bound of its size_hint() is exact.

在这种情况下，切片迭代器的下限应该是精确的，因此它应该执行一次内存移动.

In this case, the lower bound of the slice's iterator should be exact, so it should perform one memory move.

splice 更强大一点，它允许您删除一系列值(第一个参数)，插入新值(第二个参数)，并有选择地获取旧值(调用结果).

splice is a bit more powerful in that it allows you to remove a range of values (the first argument), insert new values (the second argument), and optionally get the old values (the result of the call).

替换一组项目

let mut vec = vec![0, 1, 5];
let slice = &[2, 3, 4];

vec.splice(..2, slice.iter().cloned());

println!("{:?}", vec); // [2, 3, 4, 5]

获取以前的值

let mut vec = vec![0, 1, 2, 3, 4];
let slice = &[9, 8, 7];

let old: Vec<_> = vec.splice(3.., slice.iter().cloned()).collect();

println!("{:?}", vec); // [0, 1, 2, 9, 8, 7]
println!("{:?}", old); // [3, 4]

这篇关于在 Vec 的中间或开头有效地插入或替换多个元素?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！