LeetCode-021合并两个有序链表(Merge Two Sorted Lists)

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博客围绕LeetCode-021题，要将两个有序链表合并为新的有序链表。给出示例输入输出，用Java和C实现该功能。Java实现执行用时和内存消耗表现良好，后续还将补充递归算法，博主还记录刷题情况并欢迎互勉监督。

LeetCode-021

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Example

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

Solution

Java

class ListNode {
	int val;
	ListNode next;
	ListNode(int x) { val = x; }
}
class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
    	ListNode solution=new ListNode(-1);
    	solution.next=l1;
    	ListNode node;
    	ListNode sol=solution;
    	while (l2!=null) {		//l2 -> l1
    		if (solution.next==null) {
    			solution.next=l2;
    			break;
    		}
    		if (l2.val>solution.next.val)
    			solution=solution.next;
    		else {
    			node=solution.next;
    			solution.next=new ListNode(l2.val);
    			solution.next.next=node;
    			l2=l2.next;
    		}
    	}
		return sol.next;
    }
}

C

#orderList.h
struct ListNode {
    int val;
    struct ListNode *next;
};

int comp(int a,int b);
void initList(struct ListNode **L);
void printList(struct ListNode *L);
void orderInsert(struct ListNode *L,int e,int(*compare)(int a,int b));

void insertElement(struct ListNode** L);
void initOrderlist(struct ListNode** L);

struct ListNode* mergeTwoLists(struct ListNode** l1, struct ListNode* l2);

#orderList.c
#include "stdio.h"
#include "stdlib.h"
#include "orderList.h"

/**
 *  a>b:return > 0
 *  a=b:return = 0
 *  a<b:return < 0
 *  Do not use **, return a pointer is better.
 */
int comp(int a,int b){
    return a-b;
}

int (*compare)(int a,int b) = &comp;

void printList(struct ListNode* L){
    struct ListNode* p=L;
    printf("当前链表为：\n");
    while (p->next!=NULL){
        p=p->next;
        printf("%d ",p->val);
    }
    printf("\n");
}

void initList(struct ListNode **L){
    printf("初始化链表：\n");
    struct ListNode* p=(struct ListNode*)malloc(sizeof(struct ListNode));//Head
    (*L)=p;p->val=-1;p->next=NULL;
    int index=1;
    int val=-1;
    while(1) {
        printf("退出请输入-1，请输入结点%d：\n",index);
        scanf("%d",&val);
        if (val==-1) break;
        p->next=(struct ListNode*)malloc(sizeof(struct ListNode));//Head
        p->next->val=val;p->next->next=NULL;
        p=p->next;
        index++;
    }
    printList(*L);
}

void orderInsert(struct ListNode *L,int e,int(*compare)(int a,int b)){
    struct ListNode* p=L;
    struct ListNode* q=(struct ListNode*)malloc(sizeof(struct ListNode));
    q->val=e;q->next=NULL;
    while (1){
        if (p->next==NULL){
            p->next=q;
            break;
        }
        if ((*compare)(p->next->val,e)<0)
            p=p->next;
        else{
            q->next=p->next;
            p->next=q;
            break;
        }
    }
}

void insertElement(struct ListNode** L){
    printf("在链表中插入结点：\n");
    int val=-1;
    while (1){
        printf("退出请输入-1，请输入插入结点：\n");
        scanf("%d",&val);
        if (val==-1) break;
        orderInsert(*L,val,compare);
    }
    printList(*L);
}

void initOrderlist(struct ListNode** L){
    (*L)=(struct ListNode*)malloc(sizeof(struct ListNode));
    (*L)->val=-1;(*L)->next=NULL;
    printf("初始化有序链表：\n");
    int index=1;
    int val=-1;
    while (1){
        printf("退出请输入-1，请输入结点%d：\n",index);
        scanf("%d",&val);
        if (val==-1) break;
        orderInsert(*L,val,compare);
        index++;
    }
    printList(*L);
}

struct ListNode* mergeTwoLists(struct ListNode** l1, struct ListNode* l2){
    while (l2->next!=NULL){
        l2=l2->next;
        int val=l2->val;
        orderInsert(*l1,val,compare);
    }
    return *l1;
}

#main.c
#include "orderList.h"
int main(int argc,char* argv[]){
	int op;
	struct ListNode *head1;
	struct ListNode *head2;
	printf("请选择操作类型：1、构建有序表；2、构建并向有序表中插入元素；3、构建两个有序表并将其合并为同一个；4、退出：\n");
	scanf("%d",&op);
	switch (op){
	case 1:{
	    initOrderlist(&head1);
	    break;
	}
	case 2:{
	    initOrderlist(&head1);
	    insertElement(&head1);
	    break;
	}
	case 3:{
	    initOrderlist(&head1);
	    initOrderlist(&head2);
	    printList(mergeTwoLists(&head1,head2));
	    break;
	}
	case 4:
	    exit(0);
	}
	return 0;
}