cpp-flashcards/org/cpp/deque.org

* Task: construct an empty deque :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650432
:END:
** Front
Write how to create an empty deque of ints
** Back
#+begin_src c++
std::deque<int> d;
#+end_src

* Task: construct deque with 5 copies of value :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650427
:END:
** Front
Write how to create a deque with 5 elements, all initialized to 42
** Back
#+begin_src c++
std::deque<int> d(5, 42);  // {42, 42, 42, 42, 42}
#+end_src

* Task: construct deque from initializer list :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650422
:END:
** Front
Write how to create a deque initialized with {1, 2, 3}
** Back
#+begin_src c++
std::deque<int> d = {1, 2, 3};
#+end_src

* Task: construct deque from a range :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650418
:END:
** Front
Write how to create a deque from a vector's begin/end iterators
** Back
#+begin_src c++
std::vector<int> v = {1, 2, 3, 4, 5};
std::deque<int> d(v.begin(), v.end());
#+end_src

* Task: access element at index with bounds checking :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650414
:END:
** Front
Write how to safely access element at index 2 in a deque (throws on invalid index)
** Back
#+begin_src c++
std::deque<int> d = {10, 20, 30};
int x = d.at(2);  // returns 30, throws std::out_of_range if invalid
#+end_src

* Task: access element at index with operator[] :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650409
:END:
** Front
Write how to access element at index 1 using operator[]
** Back
#+begin_src c++
std::deque<int> d = {10, 20, 30};
int x = d[1];  // returns 20, no bounds check
#+end_src

* Task: access first and last elements :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650404
:END:
** Front
Write how to get the first and last element of a deque
** Back
#+begin_src c++
std::deque<int> d = {10, 20, 30};
int first = d.front();  // 10
int last = d.back();    // 30
#+end_src

* Task: iterate over deque with begin/end :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650399
:END:
** Front
Write a range-based for loop over a deque using iterators
** Back
#+begin_src c++
std::deque<int> d = {1, 2, 3};
for (auto it = d.begin(); it != d.end(); ++it) {
    std::cout << *it << " ";
}
// or:
for (int x : d) { std::cout << x << " "; }
#+end_src

* Task: reverse iterate over deque :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650395
:END:
** Front
Write how to iterate backwards through a deque using reverse iterators
** Back
#+begin_src c++
std::deque<int> d = {1, 2, 3};
for (auto it = d.rbegin(); it != d.rend(); ++it) {
    std::cout << *it << " ";  // prints 3 2 1
}
#+end_src

* Task: check if deque is empty :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650391
:END:
** Front
Write how to check if a deque is empty
** Back
#+begin_src c++
std::deque<int> d;
if (d.empty()) { /* ... */ }
#+end_src

* Task: get size of deque :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650387
:END:
** Front
Write how to get the number of elements in a deque
** Back
#+begin_src c++
std::deque<int> d = {1, 2, 3};
std::size_t n = d.size();  // returns 3
#+end_src

* Task: clear all elements from deque :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650383
:END:
** Front
Write how to remove all elements from a deque
** Back
#+begin_src c++
std::deque<int> d = {1, 2, 3};
d.clear();  // size becomes 0
#+end_src

* Task: push elements to back of deque :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650379
:END:
** Front
Write how to add elements 10, 20, 30 to the back of a deque
** Back
#+begin_src c++
std::deque<int> d;
d.push_back(10);
d.push_back(20);
d.push_back(30);
#+end_src

* Task: push elements to front of deque :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650375
:END:
** Front
Write how to add elements 30, 20, 10 to the front of a deque (pushing in that order)
** Back
#+begin_src c++
std::deque<int> d;
d.push_front(30);  // {30}
d.push_front(20);  // {20, 30}
d.push_front(10);  // {10, 20, 30}
#+end_src

* Task: pop elements from back of deque :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650371
:END:
** Front
Write how to remove the last element from a deque
** Back
#+begin_src c++
std::deque<int> d = {1, 2, 3};
d.pop_back();  // {1, 2}
#+end_src

* Task: pop elements from front of deque :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650367
:END:
** Front
Write how to remove the first element from a deque
** Back
#+begin_src c++
std::deque<int> d = {1, 2, 3};
d.pop_front();  // {2, 3}
#+end_src

* Task: emplace back into deque :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650363
:END:
** Front
Write how to construct a pair in-place at the back of a deque (without copying)
** Back
#+begin_src c++
std::deque<std::pair<int,int>> d;
d.emplace_back(1, 2);  // constructs pair{1,2} directly
#+end_src

* Task: emplace front into deque :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650359
:END:
** Front
Write how to construct an element in-place at the front of a deque
** Back
#+begin_src c++
std::deque<std::string> d;
d.emplace_front("hello");  // constructs string directly at front
#+end_src

* Task: resize deque :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650354
:END:
** Front
Write how to resize a deque to 10 elements, filling new spots with 0
** Back
#+begin_src c++
std::deque<int> d = {1, 2, 3};
d.resize(10);        // {1, 2, 3, 0, 0, 0, 0, 0, 0, 0}
d.resize(5, 42);     // resize to 5, filling with 42 if growing
#+end_src

* Task: insert element at position :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650349
:END:
** Front
Write how to insert value 99 at the beginning of a deque
** Back
#+begin_src c++
std::deque<int> d = {1, 2, 3};
d.insert(d.begin(), 99);  // {99, 1, 2, 3}
#+end_src

* Task: insert multiple copies :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650344
:END:
** Front
Write how to insert 5 copies of value 42 starting at position begin
** Back
#+begin_src c++
std::deque<int> d = {1, 2, 3};
d.insert(d.begin(), 5, 42);  // {42, 42, 42, 42, 42, 1, 2, 3}
#+end_src

* Task: insert range into deque :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650339
:END:
** Front
Write how to insert all elements from a vector into a deque at position begin
** Back
#+begin_src c++
std::deque<int> d = {1, 2, 3};
std::vector<int> v = {10, 20};
d.insert(d.begin(), v.begin(), v.end());  // {10, 20, 1, 2, 3}
#+end_src

* Task: erase single element :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650335
:END:
** Front
Write how to erase the element at position begin + 1 in a deque
** Back
#+begin_src c++
std::deque<int> d = {1, 2, 3};
d.erase(d.begin() + 1);  // {1, 3}
#+end_src

* Task: erase range of elements :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650331
:END:
** Front
Write how to erase elements from begin to begin+2 (2 elements) in a deque
** Back
#+begin_src c++
std::deque<int> d = {1, 2, 3, 4, 5};
d.erase(d.begin(), d.begin() + 2);  // {3, 4, 5}
#+end_src

* Task: swap two deques :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650326
:END:
** Front
Write how to swap the contents of two deques
** Back
#+begin_src c++
std::deque<int> d1 = {1, 2, 3};
std::deque<int> d2 = {4, 5, 6};
d1.swap(d2);  // d1 = {4,5,6}, d2 = {1,2,3}
#+end_src

* Task: emplace at specific position :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650322
:END:
** Front
Write how to construct a pair in-place at position begin of a deque
** Back
#+begin_src c++
std::deque<std::pair<int,int>> d;
d.emplace(d.begin(), 1, 2);  // constructs pair{1,2} at begin
#+end_src

* Task: assign new contents to deque :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650318
:END:
** Front
Write how to replace all contents of a deque with 5 copies of 99
** Back
#+begin_src c++
std::deque<int> d = {1, 2, 3};
d.assign(5, 99);  // {99, 99, 99, 99, 99}
#+end_src

* Task: assign from range :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650314
:END:
** Front
Write how to replace deque contents with all elements from a vector
** Back
#+begin_src c++
std::deque<int> d;
std::vector<int> v = {10, 20, 30};
d.assign(v.begin(), v.end());  // {10, 20, 30}
#+end_src

* Task: use deque as FIFO queue :cpp:deque:production:
:PROPERTIES:
:ANKI_NOTE_TYPE: Basic
:ANKI_NOTE_ID: 1777825650305
:END:
** Front
Write how to use deque as a FIFO queue (enqueue 1, 2, 3 then dequeue all)
** Back
#+begin_src c++
std::deque<int> q;
q.push_back(1);   // enqueue
q.push_back(2);
q.push_back(3);

while (!q.empty()) {
    std::cout << q.front() << " ";
    q.pop_front();  // dequeue
}
// Output: 1 2 3
#+end_src