Rust LeetCode 练习：557 Reverse Words in a String III

时间 2019-11-05

标签 rust leetcode 练习 reverse words string iii 栏目 Microsoft Office 繁體版

原文原文链接

题目大意：输入一个以空格做为分割符的字符串，保持单词原始顺序并翻转每一个单词。性能

下面是屡次提交逐步改善代码的记录与性能数据，感谢黑化的齿轮、茶包。ui

最朴素的提交spa

pub fn reverse_words(s: String) -> String {
    let mut substrings: Vec<&str> = s.split(' ').collect();
    let mut res = String::new();
    substrings
        .iter()
        .map(|&s| {
            let bytes = unsafe { s.as_bytes() };
            let mut bytes = Vec::from(bytes);
            bytes.reverse();
            unsafe { String::from_utf8_unchecked(bytes) }
        })
        .fold(&mut res, |res, s| {
            res.push_str(s.as_str());
            res.push_str(" ");
            res
        });
    let _ = res.pop();
    res
}
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使用了move语义。内存占用没降低。code

pub fn reverse_words(s: String) -> String {
    let mut substrings: Vec<&str> = s.split(' ').collect();
    let mut res = String::new();
    substrings
        .into_iter() // move语义
        .map(|s| {
            let bytes = unsafe { s.as_bytes() };
            let mut bytes = Vec::from(bytes);
            bytes.reverse();
            unsafe { String::from_utf8_unchecked(bytes) }
        })
        .fold(&mut res, |res, s| {
            res.push_str(s.as_str());
            res.push_str(" ");
            res
        });
    let _ = res.pop();
    res
}
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代码简化：利用Slice::join替代fold()。cdn

pub fn reverse_words(s: String) -> String {
    let mut strings: Vec<&str> = s.split(' ').collect();
    strings
        .into_iter()
        .map(|s| {
            let bytes = unsafe { s.as_bytes() };
            let mut bytes = Vec::from(bytes);
            bytes.reverse();
            unsafe { String::from_utf8_unchecked(bytes) }
        })
        .collect::<Vec<_>>()
        .join(" ")
}
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代码简化：利用迭代器rec()替代Vec::reverse()。blog

pub fn reverse_words(s: String) -> String {
    let mut strings: Vec<&str> = s.split(' ').collect();
    strings
        .into_iter()
        .map(|s| {
            let byte_chars = s.bytes().rev().collect::<Vec<_>>();
            unsafe { String::from_utf8_unchecked(byte_chars) }
        })
        .collect::<Vec<_>>()
        .join(" ")
}
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代码简化：map()内部合并成一条语句。内存

pub fn reverse_words(s: String) -> String {
    s.split(' ')
        .collect::<Vec<&str>>()
        .into_iter()
        .map(|s| unsafe { String::from_utf8_unchecked(s.bytes().rev().collect::<Vec<_>>()) })
        .collect::<Vec<_>>()
        .join(" ")
}
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算法简化：利用split_mut()原地翻转。leetcode

pub fn reverse_words(s: String) -> String {
    let mut s = s.into_bytes();
    for c in s.split_mut(|&c| c == b' ') {
        c.reverse();
    }
    unsafe { String::from_utf8_unchecked(s) }
}
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代码简化：利用for_each适配器。字符串

pub fn reverse_words(s: String) -> String {
    let mut s = s.into_bytes();
    s.split_mut(|&c| c == b' ').for_each(|s| s.reverse());
    unsafe { String::from_utf8_unchecked(s) }
}
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