插入排序算法给出溢出错误

Question

当尝试运行插入排序算法时，如下所示在 Rust 1.15 中。

fn main() {
    println!("The sorted set is now: {:?}", insertion_sort(vec![5,2,4,6,1,3]));
}

fn insertion_sort(set: Vec<i32>) -> Vec<i32> {
    let mut A = set.to_vec();
    for j in 1..set.len() {
        let key = A[j];
        let mut i = j - 1;
        while (i >= 0) && (A[i] > key) {
            A[i + 1] = A[i];
            i = i - 1;
        }
        A[i + 1] = key;
    }
    A
}

我收到错误：

thread 'main' panicked at 'attempt to subtract with overflow', insertion_sort.rs:12
note: Run with `RUST_BACKTRACE=1` for a backtrace

为什么会出现溢出，如何缓解？

Answer 1

原因是您试图计算 usize 类型的 0 - 1，它是无符号的（非负数）。这可能会导致 Rust 出错。

为什么usize？因为 Rust 期望 usize 的长度和索引。您可以显式转换它们 into/from 签名的，例如isize.

fn main() {
    println!("The sorted set is now: {:?}", insertion_sort(vec![5,2,4,6,1,3]));
}

fn insertion_sort(set: Vec<i32>) -> Vec<i32> {
    let mut A = set.to_vec();
    for j in 1..set.len() as isize {
        let key = A[j as usize];
        let mut i = j - 1;
        while (i >= 0) && (A[i as usize] > key) {
            A[(i + 1) as usize] = A[i as usize];
            i = i - 1;
        }
        A[(i + 1) as usize] = key;
    }
    A
}

我推荐的另一种解决方案是完全避免负指数。在这种情况下，您可以使用 i + 1 而不是 i，如下所示：

fn main() {
    println!("The sorted set is now: {:?}", insertion_sort(vec![5,2,4,6,1,3]));
}

fn insertion_sort(set: Vec<i32>) -> Vec<i32> {
    let mut A = set.to_vec();
    for j in 1..set.len() {
        let key = A[j];
        let mut i = j;
        while (i > 0) && (A[i - 1] > key) {
            A[i] = A[i - 1];
            i = i - 1;
        }
        A[i] = key;
    }
    A
}

插入排序算法给出溢出错误

Insertion sort algorithm gives overflow error

overflow

rust