今天在 leetcode 上遇到一个 题目, 发现同样的逻辑 rust 输出错误答案。

最后把代码放到本地跑，发现 cargo run 得到正确结果，然而 cargo build --release 总是得到错误结果。

测试了一下 playground, 选 release 也是错误结果。

看起来是被过度优化了。

fn max_turbulence_size(arr: Vec<i32>) -> i32 {
    let mut prev = 0;
    let mut cnt = 0;
    let mut ret = 0;
    for w in arr.windows(2) {
        let d = w[1] - w[0];
        if d == 0 {
            cnt = 0;
        } else if d > 0 {
            if prev < 0 {
                cnt += 1;
            } else {
                cnt = 1;
            }
        } else {
            if prev > 0 {
                cnt += 1;
            } else {
                cnt = 1;
            }
        }
        // Uncomment the follow line will give the right answer
        // println!("{} {}", d, prev);
        ret = ret.max(cnt);
        // The follow line seems optimized out if we don't access `prev`, `d` simultaneously.
        prev = d;
    }
    ret + 1
}

fn main() {
    let v = vec![9,4,2,10,7,8,8,1,9];
    let ans = max_turbulence_size(v);
    // The right answer is 5. But when build with release, the output is 2
    println!("{}", ans);
}