20. 有效的括号 golang 堆栈

借用arraystack的包完成

import "github.com/emirpasic/gods/stacks/arraystack"

func isValid(s string) bool {
	stack := arraystack.New()
	for _, c := range s {
		if c == '(' {
			stack.Push(')')
		} else if c == '[' {
			stack.Push(']')
		} else if c == '{' {
			stack.Push('}')
		} else {
			if stack.Empty() {
				return false
			}
			tempC, _ := stack.Pop()
			if tempC != c {
				return false
			}
		}
	}
	return stack.Empty()
}

接下来分析一下arraystack的实现

arraystack

用法

A stack based on a array list.

ArrayStack
A stack based on a array list.

Implements Stack, IteratorWithIndex, JSONSerializer and JSONDeserializer interfaces.

package main

import "github.com/emirpasic/gods/stacks/arraystack"

func main() {
	stack := arraystack.New() // empty
	stack.Push(1)             // 1
	stack.Push(2)             // 1, 2
	stack.Values()            // 2, 1 (LIFO order)
	_, _ = stack.Peek()       // 2,true
	_, _ = stack.Pop()        // 2, true
	_, _ = stack.Pop()        // 1, true
	_, _ = stack.Pop()        // nil, false (nothing to pop)
	stack.Push(1)             // 1
	stack.Clear()             // empty
	stack.Empty()             // true
	stack.Size()              // 0
}

stack的new，push和pop

// Push adds a value onto the top of the stack
func (stack *Stack) Push(value interface{}) {
	stack.list.Add(value)
}

// Pop removes top element on stack and returns it, or nil if stack is empty.
// Second return parameter is true, unless the stack was empty and there was nothing to pop.
func (stack *Stack) Pop() (value interface{}, ok bool) {
	value, ok = stack.list.Get(stack.list.Size() - 1)
	stack.list.Remove(stack.list.Size() - 1)
	return
}


// String returns a string representation of container
func (stack *Stack) String() string {
	str := "ArrayStack\n"
	values := []string{}
	for _, value := range stack.list.Values() {
		values = append(values, fmt.Sprintf("%v", value))
	}
	str += strings.Join(values, ", ")
	return str
}

A stack based on a array list。

// Add appends a value at the end of the list
func (list *List) Add(values ...interface{}) {
	list.growBy(len(values))
	for _, value := range values {
		list.elements[list.size] = value
		list.size++
	}
}

// Get returns the element at index.
// Second return parameter is true if index is within bounds of the array and array is not empty, otherwise false.
func (list *List) Get(index int) (interface{}, bool) {
	if !list.withinRange(index) {
		return nil, false
	}
	return list.elements[index], true
}

// Remove removes the element at the given index from the list.
func (list *List) Remove(index int) {

	if !list.withinRange(index) {
		return
	}

	list.elements[index] = nil                                    // cleanup reference
	copy(list.elements[index:], list.elements[index+1:list.size]) // shift to the left by one (slow operation, need ways to optimize this)
	list.size--

	list.shrink()
}

list

// Check that the index is within bounds of the list
func (list *List) withinRange(index int) bool {
	return index >= 0 && index < list.size
}

func (list *List) resize(cap int) {
	newElements := make([]interface{}, cap, cap)
	copy(newElements, list.elements)
	list.elements = newElements
}

// Expand the array if necessary, i.e. capacity will be reached if we add n elements
func (list *List) growBy(n int) {
	// When capacity is reached, grow by a factor of growthFactor and add number of elements
	currentCapacity := cap(list.elements)
	if list.size+n >= currentCapacity {
		newCapacity := int(growthFactor * float32(currentCapacity+n))
		list.resize(newCapacity)
	}
}