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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//
// Modified into a gotemplate by Nick Craig-Wood <nick@craig-wood.com>
// Package list implements a doubly linked list.
//
// To iterate over a list (where l is a *List):
// for e := l.Front(); e != nil; e = e.Next() {
// // do something with e.Value
// }
//
package education
// template type List(A)
// ListElement is an element of a linked list.
type StudentListElement struct {
// Next and previous pointers in the doubly-linked list of elements.
// To simplify the implementation, internally a list l is implemented
// as a ring, such that &l.root is both the next element of the last
// list element (l.Back()) and the previous element of the first list
// element (l.Front()).
next, prev *StudentListElement
// The list to which this element belongs.
list *StudentList
// The value stored with this element.
Value Student
}
// Next returns the next list element or nil.
func (e *StudentListElement) Next() *StudentListElement {
if p := e.next; p != &e.list.root {
return p
}
return nil
}
// Prev returns the previous list element or nil.
func (e *StudentListElement) Prev() *StudentListElement {
if p := e.prev; p != &e.list.root {
return p
}
return nil
}
// List represents a doubly linked list.
// The zero value for List is an empty list ready to use.
type StudentList struct {
root StudentListElement // sentinel list element, only &root, root.prev, and root.next are used
len int // current list length excluding (this) sentinel element
}
// Init initializes or clears list l.
func (l *StudentList) Init() *StudentList {
l.root.next = &l.root
l.root.prev = &l.root
l.len = 0
return l
}
// New returns an initialized list.
func NewStudentList() *StudentList { return new(StudentList).Init() }
// Len returns the number of elements of list l.
func (l *StudentList) Len() int { return l.len }
// Front returns the first element of list l or nil
func (l *StudentList) Front() *StudentListElement {
if l.len == 0 {
return nil
}
return l.root.next
}
// Back returns the last element of list l or nil.
func (l *StudentList) Back() *StudentListElement {
if l.len == 0 {
return nil
}
return l.root.prev
}
// lazyInit lazily initializes a zero List value.
func (l *StudentList) lazyInit() {
if l.root.next == nil {
l.Init()
}
}
// insert inserts e after at, increments l.len, and returns e.
func (l *StudentList) insert(e, at *StudentListElement) *StudentListElement {
n := at.next
at.next = e
e.prev = at
e.next = n
n.prev = e
e.list = l
l.len++
return e
}
// insertValue is a convenience wrapper for insert(&ListElement{Value: v}, at).
func (l *StudentList) insertValue(v Student, at *StudentListElement) *StudentListElement {
return l.insert(&StudentListElement{Value: v}, at)
}
// remove removes e from its list, decrements l.len, and returns e.
func (l *StudentList) remove(e *StudentListElement) *StudentListElement {
e.prev.next = e.next
e.next.prev = e.prev
e.next = nil // avoid memory leaks
e.prev = nil // avoid memory leaks
e.list = nil
l.len--
return e
}
// Remove removes e from l if e is an element of list l.
// It returns the element value e.Value.
func (l *StudentList) Remove(e *StudentListElement) Student {
if e.list == l {
// if e.list == l, l must have been initialized when e was inserted
// in l or l == nil (e is a zero ListElement) and l.remove will crash
l.remove(e)
}
return e.Value
}
// Pushfront inserts a new element e with value v at the front of list l and returns e.
func (l *StudentList) PushFront(v Student) *StudentListElement {
l.lazyInit()
return l.insertValue(v, &l.root)
}
// PushBack inserts a new element e with value v at the back of list l and returns e.
func (l *StudentList) PushBack(v Student) *StudentListElement {
l.lazyInit()
return l.insertValue(v, l.root.prev)
}
// InsertBefore inserts a new element e with value v immediately before mark and returns e.
// If mark is not an element of l, the list is not modified.
func (l *StudentList) InsertBefore(v Student, mark *StudentListElement) *StudentListElement {
if mark.list != l {
return nil
}
// see comment in List.Remove about initialization of l
return l.insertValue(v, mark.prev)
}
// InsertAfter inserts a new element e with value v immediately after mark and returns e.
// If mark is not an element of l, the list is not modified.
func (l *StudentList) InsertAfter(v Student, mark *StudentListElement) *StudentListElement {
if mark.list != l {
return nil
}
// see comment in List.Remove about initialization of l
return l.insertValue(v, mark)
}
// MoveToFront moves element e to the front of list l.
// If e is not an element of l, the list is not modified.
func (l *StudentList) MoveToFront(e *StudentListElement) {
if e.list != l || l.root.next == e {
return
}
// see comment in List.Remove about initialization of l
l.insert(l.remove(e), &l.root)
}
// MoveToBack moves element e to the back of list l.
// If e is not an element of l, the list is not modified.
func (l *StudentList) MoveToBack(e *StudentListElement) {
if e.list != l || l.root.prev == e {
return
}
// see comment in List.Remove about initialization of l
l.insert(l.remove(e), l.root.prev)
}
// PushBackList inserts a copy of an other list at the back of list l.
// The lists l and other may be the same.
func (l *StudentList) PushBackList(other *StudentList) {
l.lazyInit()
for i, e := other.Len(), other.Front(); i > 0; i, e = i-1, e.Next() {
l.insertValue(e.Value, l.root.prev)
}
}
// PushFrontList inserts a copy of an other list at the front of list l.
// The lists l and other may be the same.
func (l *StudentList) PushFrontList(other *StudentList) {
l.lazyInit()
for i, e := other.Len(), other.Back(); i > 0; i, e = i-1, e.Prev() {
l.insertValue(e.Value, &l.root)
}
}
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