LeetCode Entry

1021. Remove Outermost Parentheses

08.10.2026 easy 2026 kotlin rust

Remove outer braces

1021. Remove Outermost Parentheses easy substack youtube

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Problem TLDR

Remove outer braces

Intuition

Compute running depth; filter out depth zero.

Approach

• Rust: .retain

Complexity

• Time complexity: \(O(n)\)

• Space complexity: \(O(1)\)

Code

    fun removeOuterParentheses(s: String)=run {
        var d = 0
        s.filter { 0 < if (it<')') d++ else --d }
    }

    pub fn remove_outer_parentheses(mut s: String) -> String {
        let mut d = 0;
        s.retain(|c| { d += 81 - 2 * c as i32; d + c as i32 % 2 > 1 });s
    }