数据结构 - 有两个链表，第一个升序，第二个降序，合并为一个升序链表（C++）

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/*
 * Created by Chimomo
 */

#include 

#define NULL 0

using namespace std;

struct Node {
    char data;
    Node *next;
};

Node *create() {
    Node *head = NULL;
    Node *rear = head;
    Node *p; // The pointer points to the new created node.
    char tmp;

    do {
        cout << "Please input integer or char '#':";
        cin >> tmp;
        if (tmp != '#') {
            p = new Node;
            p->data = tmp;
            p->next = NULL;

            if (head == NULL) {
                head = p;
            } else {
                rear->next = p;
            }

            rear = p;
        }
    } while (tmp != '#');

    return head;
}

void print(Node *head) {
    Node *p = head;
    if (head != NULL) {
        do {
            cout << p->data << ' ';
            p = p->next;
        } while (p != NULL);
    }
    cout << endl;
}

/**
 * Reverse list.
 * @param head The head pointer. Use & here since the function body changed the head pointer.
 * @return The reversed list header.
 */
Node *reverse(Node *&head) {
    if (head == NULL) {
        return NULL;
    }

    Node *pre, *cur, *ne;
    pre = head;
    cur = head->next;
    while (cur) {
        ne = cur->next; // Store next pointer.
        cur->next = pre; // Reverse the current code pointer.
        pre = cur;
        cur = ne;
    }

    head->next = NULL;
    head = pre;
    return head;
}

Node *merge(Node *l1, Node *l2) {
    Node *l2Reverse = reverse(l2);
    Node *p = new Node;
    p->next = NULL;
    Node *q = p;
    while (l1 && l2Reverse) {
        if (l1->data < l2Reverse->data) {
            p->next = l1;
            l1 = l1->next;
        } else {
            p->next = l2Reverse;
            l2Reverse = l2Reverse->next;
        }
        p = p->next;
    }

    if (l1) {
        p->next = l1;
    } else if (l2Reverse) {
        p->next = l2Reverse;
    }

    return q->next;
}

int main() {
    Node *list1 = create();
    cout << "The first list is:";
    print(list1);

    Node *list2 = create();
    cout << "The second list is:";
    print(list2);

    cout << "The merged list is:";
    Node *list = merge(list1, list2);
    print(list);

    return 0;
}

// Output:
/*
Please input integer or char '#':1
Please input integer or char '#':2
Please input integer or char '#':3
Please input integer or char '#':4
Please input integer or char '#':7
Please input integer or char '#':9
Please input integer or char '#':#
The first list is:1 2 3 4 7 9
Please input integer or char '#':8
Please input integer or char '#':6
Please input integer or char '#':5
Please input integer or char '#':4
Please input integer or char '#':2
Please input integer or char '#':1
Please input integer or char '#':#
The second list is:8 6 5 4 2 1
The merged list is:1 1 2 2 3 4 4 5 6 7 8 9

*/