合并两个排序链表--迭代和递归分别实现

题目：输入两个递增排序的链表，合并这两个链表并使新链表中的结点仍然是按照递增排序的。

#include <stdio.h>#include <malloc.h>typedef struct node{int value;struct node *next;}node,*pnode;void create_list1(pnode *head){pnode p,q;int i;for(i=1;i<9;i+=2){if(i==1){p = (pnode)malloc(sizeof(node));if(!p)return;p->value = i;p->next = NULL;*head = p;q = p;}else{p = (pnode)malloc(sizeof(node));if(!p)return;p->value = i;p->next = NULL;q->next = p;q = p;}}p = *head;printf("创建链表1为:\n");while(p){printf("%d\t",p->value);p = p->next;}printf("\n");}void create_list2(pnode *head){pnode p,q;int i;for(i=2;i<9;i+=2){if(i==2){p = (pnode)malloc(sizeof(node));if(!p)return;p->value = i;p->next = NULL;*head = p;q = p;}else{p = (pnode)malloc(sizeof(node));if(!p)return;p->value = i;p->next = NULL;q->next = p;q = p;}}p = *head;printf("创建链表2为:\n");while(p){printf("%d\t",p->value);p = p->next;}printf("\n");}pnode merge(pnode head1, pnode head2)//迭代合并{if(head1==NULL && head2==NULL)//都为空指针直接返回return NULL;else if(head1==NULL)//head1是空指针，返回head2return head2;else if(head2==NULL)//head2是空指针，返回head1return head1;pnode merge_head,p,q,m;p = head1;q = head2;if(p->value <= q->value)//确定合并后的头指针{merge_head = p;p = p->next;}else{merge_head = q;q = q->next;}m = merge_head;while(p!=NULL && q!=NULL){if(p->value <= q->value){m->next = p;m = p;p = p->next;}else{m->next = q;m = q;q = q->next;}}if(p!=NULL)//剩下的是p指针指向的链表m->next = p;if(q!=NULL)m->next = q;//剩下的是q指针指向的链表return merge_head;}pnode merge_recursion(pnode head1,pnode head2)//递归合并{if(head1==NULL && head2==NULL)return NULL;else if(head1==NULL)return head2;else if(head2==NULL)return head1;pnode merge_head;if(head1->value <= head2->value)//实质就是不断的确定头指针{merge_head = head1;merge_head->next = merge_recursion(head1->next,head2);}else{merge_head = head2;merge_head->next = merge_recursion(head1,head2->next);}return merge_head;}int main(){pnode head1, head2,merge_head;create_list1(&head1);create_list2(&head2);#if 0merge_head = merge(head1,head2);printf("迭代合并结果:\n");while(merge_head!=NULL){printf("%d\t",merge_head->value);merge_head = merge_head->next;}printf("\n");#endif#if 1merge_head = merge_recursion(head1,head2);printf("递归合并结果:\n");while(merge_head!=NULL){printf("%d\t",merge_head->value);merge_head = merge_head->next;}printf("\n");#endifreturn 0;}