parens.go

package main

import "fmt"

func isValid(x int) bool {
	s := 0
	for y := 1; y <= 0x2000; y <<= 1 {
		if x&y == 0 {
			// 0-bit means open paren, push the stack
			s++
		} else {
			// 1-bit means close paren, pop the stack
			s--
			if s < 0 {
				// detect invalid stack
				return false
			}
		}
	}
	return s == 0
}

func main() {
	c := 0
	for i := 0; i <= 0x3fff; i++ {
		if isValid(i) {
			c++
		}
	}
	fmt.Println(c)
}