0020. Valid Parentheses

Interactive visualization of bracket validation algorithms

Stack Approach
Replace Pairs Approach
Speed: 5
Stack Approach: Push opening brackets onto the stack. For each closing bracket, check if it matches the top of the stack. Time: O(n), Space: O(n)
Stack
empty
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Replace Pairs Approach: Repeatedly remove (), [], {} pairs until no more can be removed. If the string is empty, it's valid. Time: O(n²), Space: O(n)
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