题目链接
题解
#include <iostream>
#include <cstdio>
#include <vector>
#include <string>
#include <algorithm>
#include <cassert>
using namespace std;
const vector<string> OP = {
"PUSH_FRONT", "POP_FRONT", "INSERT", "CONTAINS",
"REMOVE", "REVERSE", "FOR_EACH",
"PUSH_BACK", "POP_BACK", "VISIT"};
struct Node {
int val;
Node* next;
Node* prev;
Node(): val(-1), next(nullptr), prev(nullptr) {}
Node(int x): val(x), next(nullptr), prev(nullptr) {}
};
struct List {
Node* head;
Node* tail;
List() {
head = new Node();
tail = new Node();
head->next = tail;
tail->prev = head;
}
~List() {
clear();
delete head;
delete tail;
}
void clear() {
while (head->next != tail) {
Node* a = head->next;
Node* b = a->next;
a->next = a->prev = nullptr;
delete a;
head->next = b;
b->prev = head;
}
}
void push_front(int x) {
Node* ptr = head->next;
Node* node = new Node(x);
head->next = node;
node->prev = head;
node->next = ptr;
ptr->prev = node;
}
void pop_front() {
if (head->next == tail) return;
Node* a = head->next;
Node* b = a->next;
a->prev = a->next = nullptr;
head->next = b;
b->prev = head;
delete a;
}
void insert(int index, int x) {
Node* ptr = head->next;
Node* pre = head;
for (int i = 0; i < index; i++) {
pre = ptr;
ptr = ptr->next;
}
Node* node = new Node(x);
pre->next = node;
node->prev = pre;
node->next = ptr;
ptr->prev = node;
}
bool contains(int x) {
Node* ptr = head->next;
while (ptr != tail && ptr->val != x) ptr = ptr->next;
return ptr != tail;
}
void remove(int x) {
Node* pre = head;
Node* ptr = head->next;
while (ptr != tail) {
if (ptr->val == x) {
Node* a = ptr->next;
pre->next = a;
a->prev = pre;
ptr->prev = ptr->next = nullptr;
delete ptr;
ptr = a;
} else {
pre = ptr;
ptr = ptr->next;
}
}
}
void reverse() {
Node* pre = head;
Node* ptr = head->next;
head->next = nullptr;
head->prev = ptr;
while (ptr) {
Node* node = ptr->next;
ptr->next = pre;
ptr->prev = node;
pre = ptr;
ptr = node;
}
swap(head, tail);
}
void foreach() {
Node* ptr = head->next;
for (int i = 0; ptr != tail; i++, ptr = ptr->next) {
if (i) cout << " ";
cout << ptr->val;
}
cout << endl;
}
void push_back(int x) {
Node* ptr = tail->prev;
Node* node = new Node(x);
node->prev = ptr;
ptr->next = node;
node->next = tail;
tail->prev = node;
}
void pop_back() {
if (tail->prev == head) return;
Node* a = tail->prev;
Node* b = a->prev;
b->next = tail;
tail->prev = b;
a->prev = a->next = nullptr;
delete a;
}
void visit(int x, int k) {
Node* ptr = head->next;
while (ptr != tail && ptr->val != x) ptr = ptr->next;
if (ptr == tail) {
cout << endl;
return;
}
Node* a = ptr;
for (int i = 0; i < k && a != head->next; i++) a = a->prev;
Node* b = ptr;
for (int i = 0; i <= k && b != tail; i++) b = b->next;
for (int i = 0; a != b; i++, a = a->next) {
if (i) cout << " ";
cout << a->val;
}
cout << endl;
}
};
List data;
void lpushfront() {
int x;
cin >> x;
data.push_front(x);
}
void lpopfront() {
data.pop_front();
}
void linsert() {
int index, x;
cin >> index >> x;
data.insert(index, x);
}
void lcontains() {
int x;
cin >> x;
bool ret = data.contains(x);
if (ret) cout << "true" << endl;
else cout << "false" << endl;
}
void lremove() {
int x;
cin >> x;
data.remove(x);
}
void lreverse() {
data.reverse();
}
void lforeach() {
data.foreach();
}
void lpushback() {
int x;
cin >> x;
data.push_back(x);
}
void lpopback() {
data.pop_back();
}
void lvisit() {
int x, k;
cin >> x >> k;
data.visit(x, k);
}
void solve() {
int M;
cin >> M;
data.clear();
while (M--) {
string op;
cin >> op;
int id = find(OP.begin(), OP.end(), op) - OP.begin();
switch (id) {
case 0:
lpushfront();
break;
case 1:
lpopfront();
break;
case 2:
linsert();
break;
case 3:
lcontains();
break;
case 4:
lremove();
break;
case 5:
lreverse();
break;
case 6:
lforeach();
break;
case 7:
lpushback();
break;
case 8:
lpopback();
break;
case 9:
lvisit();
break;
default:
assert(0);
}
}
}
int main() {
solve();
return 0;
}
