算法整理 & 复习：链表、双向链表

洛谷博客

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一、单向链表

1. 链表结点的定义

C++

struct ListNode{
	int data;
	ListNode *next;
};

Java

class ListNode<E>{
    E val;
    ListNode<E> next;类似
    
    ListNode(E val){
        this.val = val;
    }
}

2. 插入结点

C++

void InsertNode(ListNode *hd, ListNode *a, int x) {
	if (x == 0) {
		a->next = hd;
		hd = a;
		return;
	}
	for (int i=1;i<x && hd->next!=NULL;i++) {
		hd = hd->next;
	}
	a->next = hd->next;
	hd->next = a;
}

Java

void InsertNode(ListNode hd, ListNode, a, int x) {
	if (x == 0) {
		a.next = hd;
		hd = a;
		return;
	}
	for (int i=1;i<x && hd.next!=null;i++) {
		hd = hd.next;
	}
	a.next = hd.next;
	hd.next = a;
}

3. 删除结点

C++

ListNode *DeleteNode(ListNode *hd, int x) {
	for (int i=1;i<x;i++) {
		if (hd == NULL) return NULL;
		hd = hd->next;
	}
	ListNode *ret = hd->next;
	hd->next = hd->next->next;
	return ret;
}

Java

ListNode DeleteNode(ListNode hd, int x) {
	for (int i=1;i<x;i++) {
		if (hd == null) return null;
		hd = hd.next;
	}
	ListNode ret = hd.next;
	hd.next = hd.next.next;
	return ret;
}

4. 查找结点

C++

ListNode *FindNode(ListNode *hd, int x){
	for(int i=1;i<=x;i++){
		hd = hd->next;
	}
	return hd;
}

Java

ListNode FindNode(ListNode hd, int x) {
	for (int i=1;i<=x;i++) {
		hd = hd.next;
	}
	return hd;
}

5. 链表的逆置

ListNode *ReverseList(ListNode *hd){
	if(hd->next == NULL) return hd;
	ListNode *Rhead = NULL;
	hd = hd->next;
	while(hd != NULL){
		ListNode *temp = hd;
		hd = hd->next;
		temp->next = Rhead;
		Rhead = temp;
	}
	hd = new ListNode;
	hd->data = 0;
	hd->next = Rhead;
	return hd;
}

6. 查找倒数第 k 个结点

ListNode *kthFromEnd(ListNode *hd, int k){
	ListNode *tag = hd;
	while(k>1){
		hd = hd->next;
	}
	while(hd->next != NULL){
		hd = hd->next;
		tag = tag->next;
	}
	return tag;
}

7. 判断是否有环

ListNode *HaveLoop(ListNode *hd){
	ListNode *tag = hd;
	while(tag->next!=NULL && tag!=NULL){
		tag = tag->next->next;
		hd = hd->next;
		if(hd == tag)	return hd;
	}
	return NULL;
}

8. 查找环的入口

ListNode *FindLoopEntry(ListNode *hd){
	ListNode *tag = HaveLoop(hd);
	if(tag == NULL) return NULL;
	while(hd != tag){
		hd = hd->next;
		tag = tag->next;
	}
	return tag;
}

9. 测试程序

void PrintList(ListNode *hd){
	while(hd->next != NULL){
		hd = hd->next;
		cout << hd->data << " -> ";
	}
	cout << endl;
}

int main(void){
	ListNode *head = new ListNode;
	head->data = 0;
	head->next = NULL;
	for(int i=1;i<=5;i++){
		cin >> n;
		ListNode *Node = new ListNode;
		Node->data = n;
		Node->next = NULL;
		InsertNode(head,Node,ListLen+1);
	}
	PrintList(head);
	for(int i=1;i<=2;i++){
		cin >> n;
		DeleteNode(head,n);
		PrintList(head);
	}
	for(int i=1;i<=2;i++){
		cin >> n;
		cout << FindNode(head,n)->data << endl;
	}
	head = ReverseList(head);
	PrintList(head);
	cin >> n;
	ListNode *k = kthFromEnd(head,n);
	cout << k->data << endl;
	return 0;
}

力扣 237. 删除链表中的节点

class Solution {
    public void deleteNode(ListNode node) {
        node.val = node.next.val;
        node.next = node.next.next;
    }
}

力扣 2. 两数相加

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode head1 = l1;
        ListNode head2 = l2;
        ListNode head3 = new ListNode();
        ListNode l3 = head3;
        int k = 0;
        while (head1 != null || head2 != null) {
            int x = head1 == null ? 0 : head1.val;
            int y = head2 == null ? 0 : head2.val;
            int sum = x + y + k;
            l3.next = new ListNode(sum%10);
            k = sum / 10;
            l3 = l3.next;
            if (head1 != null) head1 = head1.next;
            if (head2 != null) head2 = head2.next;
        }
        if (k == 1) l3.next = new ListNode(1);
        return head3.next;
    }
}

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二、双向链表

1. 链表结点的定义

struct ListNode{
	int data;
	ListNode *next;
	ListNode *prev;
};

2. 插入结点

//p决定了插入到左侧还是右侧
void InsertNode(ListNode *hd, ListNode *a, int x, int p){
	if(x<=0 || x>ListLen+1) return NULL;
	for(int i=1;i<x;i++){
		hd = hd->next;
	}
	ListLen++;
	if(!p){
		a->next = hd;
		a->prev = hd->prev;
		hd->prev->next = a;
		hd->prev = a;
	}
	else{
		a->next = hd->next;
		a->prev = hd;
		hd->next->prev = a;
		hd->next = a;
	}
}

2.删除结点

ListNode *DeleteNode(ListNode *hd, int x){
	if(x<=0 || x>ListLen) return NULL;
	for(int i=1;i<x;i++){
		hd = hd->next;
	}
	ListLen--;
	ListNode *tag = hd;
	hd->prev->next = hd->next;
	hd->next->prev = hd->prev;
	return tag;
}

3. 查找结点

ListNode *FindNode(ListNode *hd, int x){
	if(x<=0 || x>ListLen) return NULL;
	for(int i=1;i<=x;i++){
		hd = hd->next;
	}
	return hd;
}

三、数组模拟双向链表

P1160 队列安排

#include <stdio.h>
#include <iostream>
using namespace std;

int a[100010][3],n,m,k,p,head=1;
//a[i][2]表示学号为i的同学右边同学的学号
//a[i][3]表示学号为i的同学左边同学的学号

int main(void){
    a[1][1] = 1;
    cin >> n;
    for(int i=2;i<=n;i++){
		cin >> k >> p;
        a[i][1] = i;
        if(p == 0){ 
            a[a[k][3]][2] = i; a[i][2] = k;
            a[i][3] = a[k][3]; a[k][3] = i;
            if(k == head) head = i;
        }
        else{
            a[a[k][2]][3] = i; a[i][3] = k;
            a[i][2] = a[k][2]; a[k][2] = i;
        }
    }
    cin >> m;
    for(int i=1;i<=m;i++){
        cin >> k;
        if(a[k][1] != 0){
            a[k][1] = 0;
            a[a[k][3]][2] = a[k][2];
            a[a[k][2]][3] = a[k][3];
            n--;
            if(k == head) head = a[k][2];
        }
    }
    while(n--){
        cout << a[head][1] << " ";
        head = a[head][2];
    }
    return 0;
}

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