From 6b9a0d3161173ef2ead4ae48cb3daae79b116016 Mon Sep 17 00:00:00 2001
From: Wong Ding Feng <dingfengwong@gmail.com>
Date: Mon, 4 May 2026 00:27:49 +0800
Subject: [PATCH] feat: add std::deque flashcards covering all member functions

---
 org/cpp/deque.org | 367 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 367 insertions(+)
 create mode 100644 org/cpp/deque.org

diff --git a/org/cpp/deque.org b/org/cpp/deque.org
new file mode 100644
index 0000000..82a4f40
--- /dev/null
+++ b/org/cpp/deque.org
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+* Task: construct an empty deque :cpp:deque:production:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
+: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
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