Problem p02265 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <iostream>
#include <stdlib.h>

using namespace std;

struct Node {
  int key;
  Node *next;
  Node *prev;
};

struct List {
  Node *nil;

  void init() {
    nil = (Node *)malloc(sizeof(Node));
    nil->next = nil;
    nil->prev = nil;
    nil->key = 0;
  }

  Node *find(int key) {
    for (Node *i = nil->next; i != nil; i = i->next) {
      if (i->key == key)
        return i;
    }
    return nil;
  }

  void insert(Node *x) {
    x->next = nil->next;
    nil->next->prev = x;
    nil->next = x;
    x->prev = nil;
  }

  void add(int x) {
    Node *p = (Node *)malloc(sizeof(Node));
    p->key = x;
    insert(p);
  }

  void delete_x(int key) {
    Node *x = find(key);
    if (x == nil)
      return;
    x->prev->next = x->next;
    x->next->prev = x->prev;
    free(x);
  }

  void deleteFirst() {
    Node *x = nil->next;
    x->prev->next = x->next;
    x->next->prev = x->prev;
    free(x);
  }

  void deleteLast() {
    Node *x = nil->prev;
    x->prev->next = x->next;
    x->next->prev = x->prev;
    free(x);
  }

  void output() {
    int flg = 0;
    for (Node *i = nil->next; i != nil; i = i->next) {
      if (flg)
        cout << ' ';
      cout << i->key;
      flg = 1;
    }
    cout << endl;
  }
};

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  List list;
  list.init();
  int n, x;
  string str;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> str;
    if (str == "insert") {
      cin >> x;
      list.add(x);
    } else if (str == "delete") {
      cin >> x;
      list.delete_x(x);
    } else if (str == "deleteFirst") {
      list.deleteFirst();
    } else {
      list.deleteLast();
    }
  }
  // cout<<'-'<<endl;
  list.output();
}

Error: TLE

Fixed submission:

#include <iostream>
#include <stdlib.h>

using namespace std;

struct Node {
  int key;
  Node *next;
  Node *prev;
};

struct List {
  Node *nil;

  void init() {
    nil = (Node *)malloc(sizeof(Node));
    nil->next = nil;
    nil->prev = nil;
    nil->key = 0;
  }

  Node *find(int key) {
    for (Node *i = nil->next; i != nil; i = i->next) {
      if (i->key == key)
        return i;
    }
    return nil;
  }

  void insert(Node *x) {
    x->next = nil->next;
    nil->next->prev = x;
    nil->next = x;
    x->prev = nil;
  }

  void add(int x) {
    Node *p = (Node *)malloc(sizeof(Node));
    p->key = x;
    insert(p);
  }

  void delete_x(int key) {
    Node *x = find(key);
    if (x == nil)
      return;
    x->prev->next = x->next;
    x->next->prev = x->prev;
    free(x);
  }

  void deleteFirst() {
    Node *x = nil->next;
    x->prev->next = x->next;
    x->next->prev = x->prev;
    free(x);
  }

  void deleteLast() {
    Node *x = nil->prev;
    x->prev->next = x->next;
    x->next->prev = x->prev;
    free(x);
  }

  void output() {
    int flg = 0;
    for (Node *i = nil->next; i != nil; i = i->next) {
      if (flg)
        cout << ' ';
      cout << i->key;
      flg = 1;
    }
    cout << endl;
  }
};

int main() {
  List list;
  list.init();
  int n, x;
  string str;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> str;
    if (str == "insert") {
      cin >> x;
      list.add(x);
    } else if (str == "delete") {
      cin >> x;
      list.delete_x(x);
    } else if (str == "deleteFirst") {
      list.deleteFirst();
    } else {
      list.deleteLast();
    }
  }
  // cout<<'-'<<endl;
  list.output();
}