ALDS1_3_C 双方向連結リストをC++で解いてみた[AIZU ONLINE JUDGE]

#include <bits/stdc++.h>
using namespace std;

struct cell {
    cell *prev;
    cell *next;
    long value;
};

class Doubly_linked_list {
    cell *nil;

  public:
    Doubly_linked_list() {
        nil = new cell;
        nil->prev = nil;
        nil->next = nil;
    }

    cell *list_search(int x) {
        cell *c = nil->next;
        while(c != nil && c->value != x) {
            c = c->next;
        }
        return c;
    }

    void print_list() {
        cell *c = nil->next;
        bool is_flag = true;
        while(true) {
            if(c == nil) {
                break;
            }
            if(is_flag == false) {
                cout << " ";
            }
            cout << c->value;
            c = c->next;
            is_flag = false;
        }
        cout << endl;
    }

    void insert(int x) {
        cell *c = new cell;
        c->value = x;
        c->prev = nil;
        c->next = nil->next;
        nil->next->prev = c;
        nil->next = c;
    }

    void delete_cell(cell *c) {
        if(c == nil) {
            return;
        }
        c->prev->next = c->next;
        c->next->prev = c->prev;
        delete c;
    }

    void delete_first() {
        delete_cell(nil->next);
    }

    void delete_last() {
        delete_cell(nil->prev);
    }

    void delete_value(int x) { delete_cell(list_search(x)); }
};

int main() {
    long n;
    cin >> n;
    Doubly_linked_list l;
    string str;
    for(int i = 0; i < n; i++) {
        cin >> str;
        if(str[0] == 'i') {
			int x;
			cin >> x;	
            l.insert(x);
        } else if(str[6] == 'F') {
            l.delete_first();
		} else if (str[6] == 'L') {
			l.delete_last();
        } else {
			int x;
			cin >> x;
            l.delete_value(x);
        }
    }

    l.print_list();
    return 0;
}