Valid Parentheses (CodeEval) in golang.

main.go

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"strings"
)

var (
	PARENTHESES = map[string]string{
		"(": ")",
		"{": "}",
		"[": "]",
	}
	OPEN_PARENTHESES  = "({["
	CLOSE_PARENTHESES = ")}]"
)

type Element struct {
	value interface{}
	next  *Element
}

type Stack struct {
	top  *Element
	size int
}

func (stack *Stack) Len() int {
	return stack.size
}

func (stack *Stack) Push(value interface{}) {
	stack.top = &Element{value, stack.top}
	stack.size++
}

func (stack *Stack) Pop() (value interface{}) {
	if stack.size > 0 {
		value, stack.top = stack.top.value, stack.top.next
		stack.size--
		return
	}
	return nil
}

func main() {
	file, err := os.Open(os.Args[1])
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {

		var parentheses string
		var is_valid bool
		stack := new(Stack)

		parentheses = scanner.Text()
		if len(parentheses) > 0 {
			is_valid = true
			for _, p := range strings.Split(parentheses, "") {
				if strings.Index(OPEN_PARENTHESES, p) != -1 {
					stack.Push(p)
					continue
				}
				if strings.Index(CLOSE_PARENTHESES, p) != -1 {
					if stack.Len() > 0 {
						last_parentheses := stack.Pop().(string)
						if PARENTHESES[last_parentheses] == p {
							continue
						}
					}
					is_valid = false
					break
				}
			}
		}

		if is_valid && stack.Len() == 0 {
			fmt.Println("True")
		} else {
			fmt.Println("False")
		}

	}
}