Question

我是Rust的新手。以下是查找两个数字的索引的代码，以便它们相加到特定目标。

use std::collections::HashMap;

fn two_sum(nums: &[i32], target: i32) -> [usize;2] {
    let mut map: HashMap<i32, usize>  = HashMap::new();

   for i in  0..nums.len() {
        let want = target - nums[i];
        match map.get(&nums[i]) {
            Some(&seen) => return [seen, i],
            _ =>  map.insert(want, i),
            };
    }

    [0usize, 0usize];
}

fn main() {
    let nums = [1,3,7,4];
    let res = two_sum(&nums, 10);
    println! ("{},{}", res[0], res[1]);
}

我收到如下错误

src/bin/2sum.rs:3:1: 15:2 error: not all control paths return a value [E0269]
src/bin/2sum.rs:3 fn two_sum(nums: &[i32], target: i32) -> [usize;2] {
src/bin/2sum.rs:4     let mut map: HashMap<i32, usize>  = HashMap::new();
src/bin/2sum.rs:5 
src/bin/2sum.rs:6     for i in  0..nums.len() {
src/bin/2sum.rs:7         let want = target - nums[i];
src/bin/2sum.rs:8         match map.get(&nums[i]) {
              ...
src/bin/2sum.rs:3:1: 15:2 help: run `rustc --explain E0269` to see a detailed     explanation
error: aborting due to previous error

那边怎么了？我该如何解决这个问题呢？

由于

Answer 1

您可以在[0usize, 0usize]（this is idiomatic）之后删除分号或添加return [0usize, 0usize]。

要改进代码，您可以返回Option。此外，在这种情况下，最好返回一个元组。

use std::collections::HashMap;

fn two_sum(nums: &[i32], target: i32) -> Option<(usize, usize)> {
    let mut map: HashMap<i32, usize> = HashMap::new();

    for i in 0..nums.len() {
        let want = target - nums[i];
        match map.get(&nums[i]) {
            Some(&seen) => return Some((seen, i)),
            _ => map.insert(want, i),
        };
    }

    None
}

fn main() {
    let nums = [1, 3, 7, 4];
    let res = two_sum(&nums, 10);
    println!("{:?}", res);
}

错误：并非所有控制路径都返回值[E0269]

1 个答案: