Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.
class Solution {
func isValid(_ s: String) -> Bool {
var chars = [Character]()
for c in s.characters {
switch c {
case "(", "[", "{":
chars.append(c)
case ")":
guard let l = chars.last, l == "(" else { return false }
chars.removeLast()
case "]":
guard let l = chars.last, l == "["else { return false }
chars.removeLast()
case "}":
guard let l = chars.last, l == "{" else { return false }
chars.removeLast()
default:
return false
}
}
return chars.isEmpty
}
}