今天學習 LinkedList
import java.util.Iterator;
import java.util.LinkedList;public class LinkedListTest {
public static void main(String[] args) {
LinkedList<String> placeToVisit = new LinkedList<String>();
placeToVisit.add("Taipei");
placeToVisit.add("New Taipei");
placeToVisit.add("Taoyuan");
placeToVisit.add("Taichung");
placeToVisit.add("Tainan");
placeToVisit.add("Kaohsiung"); printList(placeToVisit); placeToVisit.add(1, "Middle Taipei");
printList(placeToVisit); placeToVisit.remove(4);
printList(placeToVisit); } private static void printList(LinkedList<String> linkedList) {
Iterator<String> i = linkedList.iterator();
while (i.hasNext()) {
System.out.println("Now visiting City of " + i.next());
}
System.out.println("=============================");
}
}
輸出結果：
Now visiting City of Taipei
Now visiting City of New Taipei
Now visiting City of Taoyuan
Now visiting City of Taichung
Now visiting City of Tainan
Now visiting City of Kaohsiung
=============================
Now visiting City of Taipei
Now visiting City of Middle Taipei
Now visiting City of New Taipei
Now visiting City of Taoyuan
Now visiting City of Taichung
Now visiting City of Tainan
Now visiting City of Kaohsiung
=============================
Now visiting City of Taipei
Now visiting City of Middle Taipei
Now visiting City of New Taipei
Now visiting City of Taoyuan
Now visiting City of Tainan
Now visiting City of Kaohsiung
=============================
printList()
用新方法來循環，跟用 for 是一樣的
private static void printList(LinkedList<String> linkedList) {
for (String s : linkedList) {
System.out.println("Now visiting City of " + s);
}
System.out.println("=============================");
}import java.util.Iterator;
import java.util.LinkedList;
import java.util.ListIterator;public class LinkedListTest {
public static void main(String[] args) {
LinkedList<String> placeToVisit = new LinkedList<String>();
addInOrder(placeToVisit,"Taipei");
addInOrder(placeToVisit,"New Taipei");
addInOrder(placeToVisit,"Taoyuan");
addInOrder(placeToVisit,"Taichung");
addInOrder(placeToVisit,"Tainan");
addInOrder(placeToVisit,"Kaohsiung"); printList(placeToVisit); addInOrder(placeToVisit,"Taipei");
// placeToVisit.add(1, "Taipei");
// printList(placeToVisit);
//
// placeToVisit.remove(4);
// printList(placeToVisit); } private static void printList(LinkedList<String> linkedList) {
Iterator<String> i = linkedList.iterator();
while (i.hasNext()) {
System.out.println("Now visiting City of " + i.next());
}
System.out.println("=============================");
} private static boolean addInOrder(LinkedList<String> linkedList, String newCity) {
ListIterator<String> stringListIterator = linkedList.listIterator(); while (stringListIterator.hasNext()) {
int comparison = stringListIterator.next().compareTo(newCity);
if (comparison == 0) {
// equal, no add
System.out.println(newCity + " is already included as a destination");
return false;
} else if (comparison > 0) {
// new City should appear before this one
// Bcity -> Acity
stringListIterator.previous();
stringListIterator.add(newCity);
return true;
} else if (comparison < 0) {
// move on
} }
stringListIterator.add(newCity);
return true;
}
}
把加入的程式做字母順序排列
輸出結果：
Now visiting City of Kaohsiung
Now visiting City of New Taipei
Now visiting City of Taichung
Now visiting City of Tainan
Now visiting City of Taipei
Now visiting City of Taoyuan
=============================
Taipei is already included as a destination
邏輯解釋：
while (linkedlist has next element is true) {
int comparison = linkedlist go to next element,
and next element compare to parameter newCity;
compare Alphabet order(A to Z, A is smallest, Z is biggest)
if next element is Axxxx, new city is Bxxxx
comparison will be negative, because A < B
if next element is Bxxxx, new city is Axxxx
comparison will be positive, because B > A
if next element is Axxxx, new city is Axxxx
comparison will be 0, because A = B新增功能
import java.util.LinkedList;
import java.util.ListIterator;
import java.util.Scanner;public class LinkedListTest {
public static void main(String[] args) {
LinkedList<String> placeToVisit = new LinkedList<String>();
addInOrder(placeToVisit, "Taipei");
addInOrder(placeToVisit, "New Taipei");
addInOrder(placeToVisit, "Taoyuan");
addInOrder(placeToVisit, "Taichung");
addInOrder(placeToVisit, "Tainan");
addInOrder(placeToVisit, "Kaohsiung");
printList(placeToVisit); visit(placeToVisit); } private static void printList(LinkedList<String> linkedList) {
for (String s : linkedList) {
System.out.println("Now visiting City of " + s);
}
System.out.println("=============================");
} private static void addInOrder(LinkedList<String> linkedList, String newCity) {
ListIterator<String> stringListIterator = linkedList.listIterator(); while (stringListIterator.hasNext()) {
int comparison = stringListIterator.next().compareTo(newCity);
if (comparison == 0) {
// equal, no add
System.out.println(newCity + " is already included as a destination");
return;
} else if (comparison > 0) {
// new City should appear before this one
// B city -> A city
stringListIterator.previous();
stringListIterator.add(newCity);
return;
}
}
stringListIterator.add(newCity);
} private static void visit(LinkedList<String> cities) {
Scanner scanner = new Scanner(System.in);
boolean quit = false;
boolean goingForward = true;
ListIterator<String> listIterator = cities.listIterator(); if (cities.isEmpty()) {
System.out.println("No cities in the itinerary");
return;
} else {
System.out.println("Now visiting " + listIterator.next());
printMenu();
} while (!quit) {
int action = scanner.nextInt();
scanner.nextLine();
switch (action) {
case 0:
System.out.println("Vacation over!");
quit = true;
break;
case 1:
if (listIterator.hasNext()) {
System.out.println("Now visiting " + listIterator.next());
} else {
System.out.println("Reached the end of the list");
}
break;
case 2:
if (listIterator.hasPrevious()) {
System.out.println("Now visiting " + listIterator.previous());
} else {
System.out.println("We are at the start of the list");
}
break;
case 3:
printMenu();
break;
}
}
} private static void printMenu() {
System.out.println("Available actions:\npress ");
System.out.println("0 - to quit\n" +
"1 - go to next city\n" +
"2 - go to previous city\n" +
"3 - print menu options");
}
}
輸出結果：
Now visiting City of Kaohsiung
Now visiting City of New Taipei
Now visiting City of Taichung
Now visiting City of Tainan
Now visiting City of Taipei
Now visiting City of Taoyuan
=============================
Now visiting Kaohsiung
Available actions:
press
0 — to quit
1 — go to next city
2 — go to previous city
3 — print menu options
1（此行為用戶輸入）
Now visiting New Taipei
2（此行為用戶輸入）
Now visiting New Taipei
2（此行為用戶輸入）
Now visiting Kaohsiung
把城市存入 LinkedList 後
寫了一個 Method visit
可以讓訪問的城市 選擇往前往後走
但出了一個小 Bug
往前走的時候 會重複一次舊的
沒有馬上往前走
第一次輸入 2 往前走的時候
還是顯示 New Taipei
等到第二次輸入 2 才真的往前走
所以要修正
Tim 的解釋是說 是因為 LinkedList 指針沒有停留在當前元素 而是停在兩個元素之間
不過他的解釋我是看不太懂 還牽扯到了 tortoise and hare algorithm 叫我們可以自己 Google
P.S 我順便把 Tim 前面沒用到的地方照著 Intellij 的指示修正了 所以跟前面有些許不同
改 bug
import java.util.LinkedList;
import java.util.ListIterator;
import java.util.Scanner;public class LinkedListTest {
public static void main(String[] args) {
LinkedList<String> placeToVisit = new LinkedList<String>();
addInOrder(placeToVisit, "Taipei");
addInOrder(placeToVisit, "New Taipei");
addInOrder(placeToVisit, "Taoyuan");
addInOrder(placeToVisit, "Taichung");
addInOrder(placeToVisit, "Tainan");
addInOrder(placeToVisit, "Kaohsiung");
printList(placeToVisit); visit(placeToVisit); } private static void printList(LinkedList<String> linkedList) {
for (String s : linkedList) {
System.out.println("Now visiting City of " + s);
}
System.out.println("=============================");
} private static void addInOrder(LinkedList<String> linkedList, String newCity) {
ListIterator<String> stringListIterator = linkedList.listIterator(); while (stringListIterator.hasNext()) {
int comparison = stringListIterator.next().compareTo(newCity);
if (comparison == 0) {
// equal, no add
System.out.println(newCity + " is already included as a destination");
return;
} else if (comparison > 0) {
// new City should appear before this one
// B city -> A city
stringListIterator.previous();
stringListIterator.add(newCity);
return;
}
}
stringListIterator.add(newCity);
} private static void visit(LinkedList<String> cities) {
Scanner scanner = new Scanner(System.in);
boolean quit = false;
boolean goingForward = true;
ListIterator<String> listIterator = cities.listIterator(); if (cities.isEmpty()) {
System.out.println("No cities in the itinerary");
return;
} else {
System.out.println("Now visiting " + listIterator.next());
printMenu();
} while (!quit) {
int action = scanner.nextInt();
scanner.nextLine();
switch (action) {
case 0:
System.out.println("Vacation over!");
quit = true;
break;
case 1:
if (!goingForward) {
if (listIterator.hasNext()) {
listIterator.next();
}
goingForward = true;
}
if (listIterator.hasNext()) {
System.out.println("Now visiting " + listIterator.next());
} else {
System.out.println("Reached the end of the list");
goingForward = false;
}
break;
case 2:
if (goingForward) {
if (listIterator.hasPrevious()) {
listIterator.previous();
}
goingForward = false;
}
if (listIterator.hasPrevious()) {
System.out.println("Now visiting " + listIterator.previous());
} else {
System.out.println("We are at the start of the list");
goingForward = true;
}
break;
case 3:
printMenu();
break;
}
}
} private static void printMenu() {
System.out.println("Available actions:\npress ");
System.out.println("0 - to quit\n" +
"1 - go to next city\n" +
"2 - go to previous city\n" +
"3 - print menu options");
}
}
簡單的說 goingFoward 的用意就是檢測方向的改變
因為原來的代碼，當改變方向時，會重複顯示當前元素
所以寫成用 goingFoward 來判斷是否改變方向
當有改變方向，就連續往後或往前兩次，就可以規避此情況
連跳兩次，只顯示第二次的元素，這樣就不會出現重複了