feat: add iterator flashcards, sync script, and project scaffolding

- iterator.org: C++ iterator flashcard deck
- questions.org: LeetCode question index (217, 242)
- inbox.org: learning inbox with two-sum implementation and notes
- sync-anki.sh: batch sync org files to Anki via emacsclient
- AGENTS.md: conventions for AI agents working in this repo

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

AGENTS.md

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+# Agents
+
+## Repo Purpose
+C++ flashcard notes using org-mode (exportable to Anki).
+
+## Flashcard Location
+- `org/cpp/` — all flashcard `.org` files live here
+- Create new `.org` files here as needed (e.g., `org/cpp/containers.org`)
+
+## Task Inbox
+- `inbox.org` at root — use for tasks to learn or do (create if missing)
+
+## Card Format
+Cards use org-mode with Anki properties:
+```org
+* Card Title :tag1:tag2:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: TIMESTAMP
+:END:
+** Front
+Question text
+** Back
+#+begin_src c++
+code
+#+end_src
+```
+
+## Assets
+- `images/` — store any images referenced by cards
+
+## Self-Improvement
+Periodically review this file and suggest improvements to the user if you notice gaps, inconsistencies, or missing conventions.

inbox.org

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+#+title: Inbox
+* 1. two sum
+#+begin_src c++
+class Solution {
+public:
+  vector<int> twoSum(vector<int> &nums, int target) {
+    vector<pair<int, int>> rev;
+    // Fix 1 & 2: Loop over nums.size() and push nums[i]
+    for (int i = 0; i < nums.size(); i++) {
+      rev.push_back({nums[i], i});
+    }
+
+    std::sort(rev.begin(), rev.end());
+
+    for (int i = 0; i < rev.size(); i++) {
+      int want = target - rev[i].first;
+      // Fix 3: Pass the SORTED vector 'rev' to the search
+      int j = bs(rev, want, i + 1);
+      if (j >= 0) {
+        int a = rev[i].second;
+        int b = rev[j].second;
+        return vector<int>{min(a, b), max(a, b)};
+      }
+    }
+    return {};
+  }
+
+  // Updated to handle vector of pairs
+  using PairIter = vector<pair<int, int>>::iterator;
+
+  PairIter lower_bound(PairIter l, PairIter r, int target) {
+    while (l < r) {
+      PairIter mid = l + (r - l) / 2;
+      if (mid->first >= target) { // Access value via .first or ->first
+        r = mid;
+      } else {
+        l = mid + 1;
+      }
+    }
+    return l;
+  }
+
+  int bs(vector<pair<int, int>> &indexedNums, int target, int offset) {
+    auto it =
+        lower_bound(indexedNums.begin() + offset, indexedNums.end(), target);
+    if (it == indexedNums.end() || it->first != target) {
+      return -1;
+    }
+    return it - indexedNums.begin();
+  }
+};
+#+end_src
+
+~using PairIter = vector<pair<int, int>>::iterator;~
+what is using?
+
+we need to write binary search, lower bound search
+
+learn about binary search functions the natural one by god

org/cpp/iterator.org

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+* What is a C++ iterator :cpp:iterator:concept:recognition:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491263
+:END:
+** Front
+What is an iterator in C++?
+** Back
+An object that points to elements in a container and allows traversal through them, providing a common interface for accessing elements sequentially without exposing the underlying structure.
+
+* Task: Traverse a vector with iterators :cpp:iterator:production:code:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491259
+:END:
+** Front
+Write C++ code to iterate through a std::vector<int> using iterators
+** Back
+#+begin_src c++
+std::vector<int> vec = {1, 2, 3};
+for (auto it = vec.begin(); it != vec.end(); ++it) {
+    std::cout << *it << " ";
+}
+#+end_src
+
+* Iterator operations :cpp:iterator:concept:enumeration:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491255
+:END:
+** Front
+What are the four required operations for a C++ iterator?
+** Back
+- `operator*` — dereference to get current element
+- `operator++` — advance to next element (pre and post)
+- `operator==` — equality comparison
+- `operator!=` — inequality comparison
+
+* cpp iterator categories :cpp:iterator:concept:enumeration:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491250
+:END:
+** Front
+List the five iterator categories in C++ (from simplest to most advanced)
+** Back
+1. Input Iterator — read values, advance once
+2. Output Iterator — write values, advance once
+3. Forward Iterator — read/write, multiple passes
+4. Bidirectional Iterator — + operator--
+5. Random Access Iterator — + arithmetic, subscript
+
+* Task: Use const iterator :cpp:iterator:production:code:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491246
+:END:
+** Front
+Write C++ code to safely traverse a const std::vector without modifying elements
+** Back
+#+begin_src c++
+std::vector<int> vec = {1, 2, 3};
+for (auto it = vec.cbegin(); it != vec.cend(); ++it) {
+    std::cout << *it << " ";
+}
+#+end_src
+
+* Task: Use reverse iterator :cpp:iterator:production:code:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491241
+:END:
+** Front
+Write C++ code to iterate backwards through a std::vector
+** Back
+#+begin_src c++
+std::vector<int> vec = {1, 2, 3};
+for (auto it = vec.rbegin(); it != vec.rend(); ++it) {
+    std::cout << *it << " ";
+}
+#+end_src
+
+* Minimal custom iterator implementation :cpp:iterator:implementation:production:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491237
+:END:
+** Front
+Write the minimal C++ code to implement a forward iterator for a custom class
+** Back
+#+begin_src c++
+class MyIterator {
+    Node* ptr;
+public:
+    reference operator*() const { return ptr->data; }
+    pointer operator->() const { return &ptr->data; }
+    MyIterator& operator++() { ptr = ptr->next; return *this; }
+    MyIterator operator++(int) { auto tmp = *this; ++*this; return tmp; }
+    bool operator==(const MyIterator& other) const { return ptr == other.ptr; }
+    bool operator!=(const MyIterator& other) const { return !(*this == other); }
+};
+#+end_src
+
+* When to use iterators vs indices :cpp:iterator:concept:comparison:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491226
+:END:
+** Front
+When would you choose iterators over index-based loops in C++?
+** Back
+- Container type is unknown or could change (iterators abstract the container)
+- Using standard library algorithms (std::find, std::sort, etc.)
+- Need to traverse multiple containers simultaneously
+- Working with containers without random access (list, map)
+- Decouple algorithm from container structure

org/cpp/questions.org

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+#+title: Questions
+* 217
+* 242 valid anagrams

org/org-syntax.org

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+# Org-Mode Syntax Reference
+
+This document covers org-mode syntax for creating flashcards.
+
+* Headlines
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you create headlines in org-mode?
+** Back
+=* Heading 1= (one asterisk)
+=** Heading 2= (two asterisks)
+=*** Heading 3= (etc.)
+
+#+begin_src org
+* Top Level
+** Second Level
+*** Third Level
+#+end_src
+
+* Emphasis
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you bold, italic, and code in org-mode?
+** Back
+=*bold*= :: *bold*
+=/italic /= :: /italic/
+=~code~= :: ~code~ (inline code, like backticks)
+==verbatim== :: =verbatim= (literal text)
+=_underline_= :: _underline_
+
+* Code Blocks
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you write a source code block in org-mode?
+** Back
+#+begin_src org
+#+begin_src cpp
+std::vector<int> v;
+#+end_src
+#+end_src
+
+Supported languages: =cpp=, =c=, =python=, =bash=, =javascript=, =sql=, =json=, =html=, =css=, =rust=, =go=, etc.
+
+* Links
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you write links in org-mode?
+** Back
+#+begin_src org
+[[https://example.com][Description]]
+[[https://example.com]]  (auto-named)
+[[file:path/to/file.org][Local file]]
+#+end_src
+
+* External Links
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you link to external URLs in org-mode?
+** Back
+Plain URL or with description:
+#+begin_src org
+https://example.com
+[[https://example.com][Example Site]]
+#+end_src
+
+* Lists
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you write bullet and numbered lists in org-mode?
+** Back
+#+begin_src org
+- Bullet item
+- Another item
+  - Sub-item (indent with spaces)
+
+1. Numbered item
+2. Second item
+
+- [ ] Unchecked task
+- [X] Checked task
+#+end_src
+
+* Properties Drawer
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you add properties to a flashcard heading?
+** Back
+#+begin_src org
+* Card Title :tag1:tag2:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1234567890
+:END:
+** Front
+Question
+** Back
+Answer
+#+end_src
+
+Properties drawer goes directly after the heading, before Front.
+
+* Tags
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you add tags to a headline?
+** Back
+Tags go after the heading, separated by colons:
+#+begin_src org
+* My Card :cpp:containers:stl:
+#+end_src
+
+Tags can be inherited by subheadings.
+
+* Flashcard Structure
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+What is the complete structure of an org-mode flashcard?
+** Back
+#+begin_src org
+* Question/Title :tag:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+The question or prompt
+** Back
+The answer (often includes source blocks)
+
+#+begin_src cpp
+code here
+#+end_src
+#+end_src
+
+* Export Blocks
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you create a block that exports to a specific format?
+** Back
+#+begin_src org
+#+begin_export html
+HTML content here
+#+end_export
+
+#+begin_export latex
+LaTeX content here
+#+end_export
+#+end_src
+
+* Comments
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you add comments in org-mode?
+** Back
+#+begin_src org
+#+COMMENT: This entire line is a comment
+
+# Also a comment (headline-level)
+#+end_src
+
+* Block Quotes
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you create a block quote in org-mode?
+** Back
+#+begin_src org
+#+begin_quote
+Your quote text here.
+It can span multiple lines.
+#+end_quote
+#+end_src
+
+* Example Blocks
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you create an example block (literal text)?
+** Back
+#+begin_src org
+#+begin_example
+This text is literal - no emphasis processing.
+*not bold*
+#+end_example
+#+end_src
+
+* Horizontal Rules
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you create a horizontal rule in org-mode?
+** Back
+Five or more dashes:
+#+begin_src org
+-----
+#+end_src
+
+* Tables
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you create a table in org-mode?
+** Back
+#+begin_src org
+| Header 1 | Header 2 |
+|----------+----------|
+| Cell 1   | Cell 2   |
+| Cell 3   | Cell 4   |
+#+end_src
+
+Tables need at least one dash in the separator row.
+
+* footnotes
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you add footnotes in org-mode?
+** Back
+#+begin_src org
+Some text with a footnote[fn:1]
+
+[fn:1] This is the footnote content.
+#+end_src
+
+* Special Symbols
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you insert special symbols in org-mode?
+** Back
+Using org-entities:
+#+begin_src org
+\alpha → \alpha
+\beta  → \beta
+\sum   → \sum
+\pm    → \pm
+\rightarrow → \rightarrow
+#+end_src
+
+Also works: =\egal= (𝑎𝑏𝑐), =~abc~= (code)
+
+* Todo States
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you mark a headline as a todo item?
+** Back
+#+begin_src org
+TODO Some task
+DONE Completed task
+#+end_src
+
+Common states: =TODO=, =DONE=, =NEXT=, =WAITING=, =CANCELLED=
+
+* Radio Targets
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+What is a radio target in org-mode?
+** Back
+Links that jump to specific locations in the same file:
+#+begin_src org
+<<target name>>
+
+[[target name]] or [[*target name]]
+#+end_src
+
+* Statistics Cookies
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:END:
+** Front
+How do you show task progress in org-mode?
+** Back
+#+begin_src org
+[50%]    - percentage
+[3/5]    - completed/total
+#+end_src
+
+Often used in lists like: =[- 2/5]=

sync-anki.sh

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+#!/usr/bin/env bash
+# Sync org files to Anki using emacsclient
+
+set -euo pipefail
+
+FILES=(
+    "org/cpp/iterator.org"
+    "org/cpp/containers.org"
+    # add more files here
+)
+
+for file in "${FILES[@]}"; do
+    if [[ -f "$file" ]]; then
+        echo "Syncing $file..."
+        emacsclient --eval "(progn (find-file \"$file\") (org-anki-sync-all))"
+    else
+        echo "File not found: $file" >&2
+    fi
+done
+
+echo "Done."