[Swift] Valid Parentheses

Valid Parentheses

Given a string s containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[’ and ‘]’, determine if the input string is valid. An input string is valid if:

1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.

Example

Input: s = "()"
Output: true

Input: s = "()[]{}"
Output: true

Input: s = "(]"
Output: false

Input: s = "([)]"
Output: false

Input: s = "{[]}"
Output: true

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문제 이해

코드

func isValid(_ s: String) -> Bool {
    var stack: [Character] = []

    if s.count == 1 {
        return false
    }
    for c in s {
        if c == "(" {
            stack.append(")")
        } else if c == "[" {
            stack.append("]")
        } else if c == "{" {
            stack.append("}")
        } else {
            if !stack.isEmpty {
                let pop = stack.removeLast()
                if pop != c {
                    return false
                }
            } else {
                return false
            }
        }
    }

    return stack.isEmpty
}

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