c_cpp 链接列表的合并排序

Posted 2021-05-14

// https://www.geeksforgeeks.org/merge-sort-for-linked-list/
#include <iostream>
#include <list>
using namespace std;

struct linked_list {
    int data;
    struct linked_list *next;
};
typedef struct linked_list node;

void print (node *n) {
    while (n) {
        cout<< n->data<< "->";
        n = n->next;
    }
    cout<< "NULL";
    return;
}

void insert(node **headref, int n) {
    node* last = *headref;
    node *temp=new node;

    temp->data = n;
    temp->next=NULL;
    if (last == NULL) {
        *headref = temp;
        return;
    }
    while (last->next)
        last = last->next;
    last->next = temp;
    return;
}

void split(node *head, node **aref, node **bref) {
    node *fast=head->next, *slow=head;
    while(fast) {
        fast = fast->next;
        if (fast != NULL) {
            fast = fast->next;
            slow = slow->next;
        }
    }
    *aref = head;
    *bref = slow->next;
    slow->next = NULL;
    return;
}

node* merge(node *a, node *b) {
    node *head = NULL;
    while (a && b) {
        if (a->data <= b->data) {
            insert(&head, a->data);
            a = a->next;
        }
        else {
            insert(&head, b->data);
            b = b->next;
        }
    }
    while (a) {
        insert(&head, a->data);
        a = a->next;
    }
    while (b) {
        insert(&head, b->data);
        b = b->next;
    }
    return head;
}

void MergeSort(node** headref) {
    node *head = *headref;
    node *a, *b;
    if (head == NULL || head->next == NULL)
        return;
    split(head,&a,&b);
    MergeSort(&a);
    MergeSort(&b);
    *headref=merge(a,b);
    return;
}

int main() {
    int n;
    node *head=NULL;
    while (true) {
        cout<< "Enter the number: ";
        cin>>n;
        if (n==-9)
            break;
        else
            insert(&head,n);
    }
    print(head);
    MergeSort(&head);
    cout<< "\nSorted List is:\n";
    print(head);
}