stack

package main

import (
    "errors"
    "log"
)

// 简单的栈定义
// go run stack.go n_xxx.go
type Stack []int

func (s *Stack) Len() int {
    return len(*s)
}

func (s *Stack) IsEmpty() bool {
    return s.Len() == 0
}

func (s *Stack) Push(elem int) {
    *s = append(*s, elem)
}

var ERR_STACK_EMPTY = errors.New("stack is empty")

func (s *Stack) Pop() int {
    n := s.Len()
    if n == 0 {
        log.Fatal(ERR_STACK_EMPTY)
    }
    peek := (*s)[n-1]
    *s = (*s)[:n-1]
    return peek
}

func (s *Stack) Peek() int {
    n := s.Len()
    if n == 0 {
        log.Fatal(ERR_STACK_EMPTY)
    }
    return (*s)[n-1]
}