Rust代码
```rust
const ELEMS: [&str; 4] = ["A", "B", "C", "D"];

fn main() {
    let combinations = generate_combinations(&ELEMS, 0, "");
    println!("Combinations: {:?}", combinations);
}

fn generate_combinations(elems: &[&str], start: usize, prefix: &str) -> Vec<String> {
    let mut combinations = Vec::new();

    for i in start..elems.len() {
        let new_prefix = prefix.to_string() + elems[i];
        combinations.extend(generate_combinations(elems, i + 1, &new_prefix));
        combinations.push(new_prefix);
    }

    combinations
}
```

这是递归，但对栈有压力
如果不想递归，遍历用2^N种可能的0-1组合，直接扁平化去做
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