package q20

func isValid(s string) bool {
	stack := make([]byte, 0, len(s)/2)

	for i := range len(s) {
		switch s[i] {
		case '(', '[', '{':
			stack = append(stack, s[i])
		case ')':
			if len(stack) == 0 || stack[len(stack)-1] != '(' {
				return false
			}
			stack = stack[:len(stack)-1]

		case ']':
			if len(stack) == 0 || stack[len(stack)-1] != '[' {
				return false
			}
			stack = stack[:len(stack)-1]

		case '}':
			if len(stack) == 0 || stack[len(stack)-1] != '{' {
				return false
			}
			stack = stack[:len(stack)-1]
		}
	}
	return len(stack) == 0
}

var _ = isValid