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Commit 656ea48

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Merge pull request youngyangyang04#2818 from donghuanjie/master
707代码规范化,添加部分comments; 203添加了java版本的递归
2 parents 8d4d810 + cc1cdb0 commit 656ea48

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‎problems/0203.移除链表元素.md

Lines changed: 31 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -337,6 +337,37 @@ public ListNode removeElements(ListNode head, int val) {
337337

338338
```
339339

340+
递归
341+
342+
```java
343+
/**
344+
* 时间复杂度 O(n)
345+
* 空间复杂度 O(n)
346+
* @param head
347+
* @param val
348+
* @return
349+
*/
350+
class Solution {
351+
public ListNode removeElements(ListNode head, int val) {
352+
if (head == null) {
353+
return head;
354+
}
355+
356+
// 假设 removeElements() 返回后面完整的已经去掉val节点的子链表
357+
// 在当前递归层用当前节点接住后面的子链表
358+
// 随后判断当前层的node是否需要被删除,如果是,就返回
359+
// 也可以先判断是否需要删除当前node,但是这样条件语句会比较不好想
360+
head.next = removeElements(head.next, val);
361+
if (head.val == val) {
362+
return head.next;
363+
}
364+
return head;
365+
366+
// 实际上就是还原一个从尾部开始重新构建链表的过程
367+
}
368+
}
369+
```
370+
340371
### Python:
341372

342373
```python

‎problems/0707.设计链表.md

Lines changed: 63 additions & 65 deletions
Original file line numberDiff line numberDiff line change
@@ -422,38 +422,38 @@ void myLinkedListFree(MyLinkedList* obj) {
422422
423423
```Java
424424
//单链表
425-
class ListNode {
426-
int val;
427-
ListNode next;
428-
ListNode(){}
429-
ListNode(int val) {
430-
this.val=val;
431-
}
432-
}
433425
class MyLinkedList {
426+
427+
class ListNode {
428+
int val;
429+
ListNode next;
430+
ListNode(int val) {
431+
this.val=val;
432+
}
433+
}
434434
//size存储链表元素的个数
435-
int size;
436-
//虚拟头结点
437-
ListNode head;
435+
private int size;
436+
//注意这里记录的是虚拟头结点
437+
private ListNode head;
438438
439439
//初始化链表
440440
public MyLinkedList() {
441-
size = 0;
442-
head = new ListNode(0);
441+
this.size = 0;
442+
this.head = new ListNode(0);
443443
}
444444
445-
//获取第index个节点的数值,注意index是从0开始的,第0个节点就是头结点
445+
//获取第index个节点的数值,注意index是从0开始的,第0个节点就是虚拟头结点
446446
public int get(int index) {
447447
//如果index非法,返回-1
448448
if (index < 0 || index >= size) {
449449
return -1;
450450
}
451-
ListNode currentNode = head;
452-
//包含一个虚拟头节点,所以查找第 index+1 个节点
451+
ListNode cur = head;
452+
//第0个节点是虚拟头节点,所以查找第 index+1 个节点
453453
for (int i = 0; i <= index; i++) {
454-
currentNode = currentNode.next;
454+
cur = cur.next;
455455
}
456-
return currentNode.val;
456+
return cur.val;
457457
}
458458
459459
public void addAtHead(int val) {
@@ -473,7 +473,6 @@ class MyLinkedList {
473473
while (cur.next != null) {
474474
cur = cur.next;
475475
}
476-
477476
cur.next = newNode;
478477
size++;
479478
@@ -485,81 +484,79 @@ class MyLinkedList {
485484
// 如果 index 等于链表的长度,则说明是新插入的节点为链表的尾结点
486485
// 如果 index 大于链表的长度,则返回空
487486
public void addAtIndex(int index, int val) {
488-
if (index > size) {
487+
if (index < 0 || index > size) {
489488
return;
490489
}
491-
if (index < 0) {
492-
index = 0;
493-
}
494-
size++;
490+
495491
//找到要插入节点的前驱
496-
ListNode pred = head;
492+
ListNode pre = head;
497493
for (int i = 0; i < index; i++) {
498-
pred = pred.next;
494+
pre = pre.next;
499495
}
500-
ListNode toAdd = new ListNode(val);
501-
toAdd.next = pred.next;
502-
pred.next = toAdd;
496+
ListNode newNode = new ListNode(val);
497+
newNode.next = pre.next;
498+
pre.next = newNode;
499+
size++;
503500
}
504501
505-
//删除第index个节点
506502
public void deleteAtIndex(int index) {
507503
if (index < 0 || index >= size) {
508504
return;
509505
}
510-
size--;
511-
//因为有虚拟头节点,所以不用对Index=0的情况进行特殊处理
512-
ListNode pred = head;
506+
507+
//因为有虚拟头节点,所以不用对index=0的情况进行特殊处理
508+
ListNode pre = head;
513509
for (int i = 0; i < index ; i++) {
514-
pred = pred.next;
510+
pre = pre.next;
515511
}
516-
pred.next = pred.next.next;
512+
pre.next = pre.next.next;
513+
size--;
517514
}
518515
}
516+
```
519517

518+
```Java
520519
//双链表
521-
class ListNode{
522-
int val;
523-
ListNode next,prev;
524-
ListNode() {};
525-
ListNode(int val){
526-
this.val = val;
527-
}
528-
}
529-
530-
531520
class MyLinkedList {
532521

522+
class ListNode{
523+
int val;
524+
ListNode next, prev;
525+
ListNode(int val){
526+
this.val = val;
527+
}
528+
}
529+
533530
//记录链表中元素的数量
534-
int size;
531+
privateint size;
535532
//记录链表的虚拟头结点和尾结点
536-
ListNode head,tail;
533+
privateListNode head,tail;
537534

538535
public MyLinkedList() {
539536
//初始化操作
540537
this.size = 0;
541538
this.head = new ListNode(0);
542539
this.tail = new ListNode(0);
543540
//这一步非常关键,否则在加入头结点的操作中会出现null.next的错误!!!
544-
head.next=tail;
545-
tail.prev=head;
541+
this.head.next=tail;
542+
this.tail.prev=head;
546543
}
547544

548545
public int get(int index) {
549546
//判断index是否有效
550-
if(index>=size){
547+
if(index<0|| index >=size){
551548
return -1;
552549
}
553-
ListNode cur = this.head;
550+
ListNode cur = head;
554551
//判断是哪一边遍历时间更短
555552
if(index >= size / 2){
556553
//tail开始
557554
cur = tail;
558-
for(int i=0; i< size-index; i++){
555+
for(int i=0; i< size-index; i++){
559556
cur = cur.prev;
560557
}
561558
}else{
562-
for(int i=0; i<= index; i++){
559+
for(int i=0; i<= index; i++){
563560
cur = cur.next;
564561
}
565562
}
@@ -568,24 +565,23 @@ class MyLinkedList {
568565

569566
public void addAtHead(int val) {
570567
//等价于在第0个元素前添加
571-
addAtIndex(0,val);
568+
addAtIndex(0,val);
572569
}
573570

574571
public void addAtTail(int val) {
575572
//等价于在最后一个元素(null)前添加
576-
addAtIndex(size,val);
573+
addAtIndex(size,val);
577574
}
578575

579576
public void addAtIndex(int index, int val) {
580-
//index大于链表长度
581-
if(index>size){
577+
//判断index是否有效
578+
if(index<0|| index >size){
582579
return;
583580
}
584581

585-
size++;
586582
//找到前驱
587-
ListNode pre = this.head;
588-
for(int i=0; i<index; i++){
583+
ListNode pre = head;
584+
for(int i=0; i<index; i++){
589585
pre = pre.next;
590586
}
591587
//新建结点
@@ -594,22 +590,24 @@ class MyLinkedList {
594590
pre.next.prev = newNode;
595591
newNode.prev = pre;
596592
pre.next = newNode;
593+
size++;
597594

598595
}
599596

600597
public void deleteAtIndex(int index) {
601-
//判断索引是否有效
602-
if(index>=size){
598+
//判断index是否有效
599+
if(index<0|| index >=size){
603600
return;
604601
}
602+
605603
//删除操作
606-
size--;
607-
ListNode pre = this.head;
608-
for(int i=0; i<index; i++){
604+
ListNode pre = head;
605+
for(int i = 0; i < index; i++){
609606
pre = pre.next;
610607
}
611608
pre.next.next.prev = pre;
612609
pre.next = pre.next.next;
610+
size--;
613611
}
614612
}
615613

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