iOS Interview - Leetcode 20: Valid Parentheses

April 26, 2024 • 1 min read • #swift, #interview, #leetcode

Primary idea: Use a stack to see whether the peek left brace is correspond to the current right one
Time Complexity: O(n)
Space Complexity: O(n)

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

    for char in s {
        switch char {
        case "(", "[", "{":
            stack.append(char)
        case ")":
            if stack.popLast() != "(" {
                return false
            }
        case "]":
            if stack.popLast() != "[" {
                return false
            }
        case "}":
            if stack.popLast() != "{" {
                return false
            }
        default:
            continue
        }
    }

    return true
}

print(isValidParentheses("()")) // true
print(isValidParentheses("()[]{}")) // true
print(isValidParentheses("(]")) // false