g0001_0100.s0020_valid_parentheses.Solution.swift Maven / Gradle / Ivy

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104 LeetCode algorithm problem solutions

There is a newer version: 1.8

// #Easy #Top_100_Liked_Questions #Top_Interview_Questions #String #Stack
// #Data_Structure_I_Day_9_Stack_Queue #Udemy_Strings #Big_O_Time_O(n)_Space_O(n)
// #2024_06_18_Time_0_ms_(100.00%)_Space_16.3_MB_(43.79%)

class Solution {
    func isValid(_ s: String) -> Bool {
        var stack = [Character]()
        
        for char in s {
            if char == "(" || char == "[" || char == "{" {
                stack.append(char)
            } else if char == ")" && !stack.isEmpty && stack.last == "(" {
                stack.popLast()
            } else if char == "}" && !stack.isEmpty && stack.last == "{" {
                stack.popLast()
            } else if char == "]" && !stack.isEmpty && stack.last == "[" {
                stack.popLast()
            } else {
                return false
            }
        }
        
        return stack.isEmpty
    }
}