Leetcode_problems: merge feat/upgrade into main

.clang-format

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+# clang-format config for the C++ solution snippets.
+# These are bare LeetCode editor bodies (no includes), so formatting is the only
+# whole-file check that's meaningful; the syntax gate handles correctness.
+BasedOnStyle: Google
+IndentWidth: 4
+TabWidth: 4
+UseTab: Never
+ColumnLimit: 100
+AllowShortFunctionsOnASingleLine: Empty
+AllowShortIfStatementsOnASingleLine: false
+AllowShortLoopsOnASingleLine: false
+SortIncludes: false

.coderabbit.yaml

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+# CodeRabbit config — lightweight, archive-appropriate.
+language: en-US
+reviews:
+  profile: chill
+  request_changes_workflow: false
+  high_level_summary: true
+  poem: false
+  review_status: true
+  path_filters:
+    - "!solutions/**"  # don't nitpick historical submission snippets
+    - "scripts/**"
+    - ".github/**"
+    - "*.md"
+chat:
+  auto_reply: true

.gitattributes

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+# Keep LF for scripts and config so CI bash/Python behave identically on all OSes.
+* text=auto eol=lf
+*.png binary
+*.jpg binary
+*.svg text eol=lf

.github/FUNDING.yml

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+github: [aliammari1]

.github/ISSUE_TEMPLATE/solution_issue.md

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+---
+name: Solution issue
+about: Report an incorrect solution or suggest an improvement
+title: "[slug] short description"
+labels: ["solution"]
+---
+
+**Problem slug:** <!-- e.g. two-sum (the directory name under solutions/) -->
+
+**Language:** <!-- C++ / Java / Oracle SQL / MySQL -->
+
+**What's wrong / what could be better?**
+
+<!-- Note: failed-attempt snippets (Wrong Answer/Runtime Error/etc.) are kept on
+purpose as part of the submission history; please don't report those as bugs. -->

.github/dependabot.yml

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+version: 2
+# Archive repo: the only moving dependencies are GitHub Actions and the docs
+# build tooling (requirements-docs.txt). Dependabot is the single dependency
+# bot here — a Renovate config was removed to avoid duplicate update PRs.
+updates:
+  - package-ecosystem: github-actions
+    directory: "/"
+    schedule:
+      interval: weekly
+    commit-message:
+      prefix: "ci"
+    labels: ["dependencies"]
+    groups:
+      github-actions:
+        patterns: ["*"]
+
+  - package-ecosystem: pip
+    directory: "/"
+    schedule:
+      interval: weekly
+    commit-message:
+      prefix: "build"
+    labels: ["dependencies"]

.github/workflows/ai-explain.yml

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+name: AI solution explanations
+
+on:
+  workflow_dispatch:
+    inputs:
+      limit:
+        description: "Max number of slugs to process (0 = all)"
+        default: "20"
+      force:
+        description: "Overwrite existing EXPLANATION.md"
+        type: boolean
+        default: false
+  schedule:
+    # Weekly top-up of any newly-added Accepted solutions lacking an explanation.
+    - cron: "0 5 * * 1"
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  explain:
+    name: Generate EXPLANATION.md with Claude
+    runs-on: ubuntu-latest
+    # Gated: the job only runs when ANTHROPIC_API_KEY is configured.
+    if: ${{ vars.ENABLE_AI == 'true' || github.event_name == 'workflow_dispatch' }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install Anthropic SDK
+        run: pip install "anthropic>=0.40"
+
+      - name: Generate explanations (with WA/RE diff hook)
+        env:
+          ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
+          AI_MODEL: ${{ vars.AI_MODEL || 'claude-sonnet-4-6' }}
+        run: |
+          # Script is a no-op when ANTHROPIC_API_KEY is unset, so this is safe
+          # to run on PRs / forks without the secret.
+          ARGS="--tag --limit ${{ github.event.inputs.limit || '20' }}"
+          if [ "${{ github.event.inputs.force }}" = "true" ]; then ARGS="$ARGS --force"; fi
+          python scripts/ai_explain.py $ARGS
+
+      - name: Open PR with new explanations
+        if: ${{ env.HAS_KEY == 'true' }}
+        env:
+          HAS_KEY: ${{ secrets.ANTHROPIC_API_KEY != '' }}
+        uses: peter-evans/create-pull-request@v6
+        with:
+          commit-message: "docs: add AI-generated solution explanations"
+          title: "docs: AI solution explanations"
+          body: |
+            Auto-generated `EXPLANATION.md` files (approach, complexity, and a
+            diff vs the recorded Wrong-Answer / Runtime-Error attempts).
+            Review before merging.
+          branch: ai/explanations
+          add-paths: |
+            solutions/**/EXPLANATION.md

.github/workflows/ci.yml

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+name: CI
+
+on:
+  push:
+    branches: [main, master]
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ci-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  progress:
+    name: Progress table is current
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      # Fails if README's PROGRESS block or docs/progress.json drifted from
+      # solutions/ — keeps the 173-vs-542 stats honest and reconciled.
+      - name: Check generated stats
+        run: python scripts/generate_progress.py --check
+
+  cpp-syntax:
+    name: C++ preamble-injection syntax gate
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - name: Install g++
+        run: sudo apt-get update && sudo apt-get install -y g++
+      # Injects `#include <bits/stdc++.h>` + `using namespace std;` then runs
+      # g++ -fsyntax-only. Real errors fail the build (no `|| echo`).
+      - name: Syntax-check all Accepted C++ solutions
+        run: python scripts/compile_check.py --cxx g++ --std c++20
+
+  clang-format:
+    name: clang-format
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: clang-format check (quoted globs)
+        run: |
+          # Paths contain spaces and commas — NUL-delimit and quote.
+          mapfile -d '' files < <(find solutions -type f -name 'Solution.cpp' -print0)
+          if [ ${#files[@]} -eq 0 ]; then echo "no C++ files"; exit 0; fi
+          clang-format --dry-run --Werror "${files[@]}"
+
+  cpp-linter:
+    name: cpp-linter
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cpp-linter/cpp-linter-action@v2
+        id: linter
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          style: file
+          tidy-checks: "-*" # format-only; bare snippets have no compile DB
+          files-changed-only: false
+          extensions: cpp
+      - name: Fail on lint findings
+        if: steps.linter.outputs.checks-failed > 0
+        run: exit 1
+
+  sql:
+    name: sqlfluff (Oracle + MySQL)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - name: Install sqlfluff
+        run: pip install "sqlfluff==3.3.0"
+      - name: Lint Oracle SQL (quoted globs)
+        run: |
+          mapfile -d '' files < <(find solutions -type f -name '*.oraclesql' -print0)
+          if [ ${#files[@]} -eq 0 ]; then echo "no Oracle SQL"; exit 0; fi
+          sqlfluff lint --dialect oracle "${files[@]}"
+      - name: Lint MySQL (quoted globs)
+        run: |
+          mapfile -d '' files < <(find solutions -type f -name '*.mysql' -print0)
+          if [ ${#files[@]} -eq 0 ]; then echo "no MySQL"; exit 0; fi
+          sqlfluff lint --dialect mysql "${files[@]}"
+
+  docs:
+    name: mkdocs build (strict)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - name: Install docs deps
+        run: pip install -r requirements-docs.txt
+      - name: Generate pages
+        run: python scripts/generate_progress.py --docs
+      - name: Build
+        run: mkdocs build --strict

.github/workflows/claude-review.yml

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+name: Claude PR review
+
+on:
+  pull_request:
+    types: [opened, synchronize]
+  issue_comment:
+    types: [created]
+
+permissions:
+  contents: read
+  pull-requests: write
+  issues: write
+
+jobs:
+  review:
+    name: "@claude review"
+    runs-on: ubuntu-latest
+    # Gated on the secret: skips cleanly when ANTHROPIC_API_KEY is absent.
+    if: ${{ github.event_name == 'pull_request' || contains(github.event.comment.body, '@claude') }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: Claude Code Action
+        uses: anthropics/claude-code-action@v1
+        with:
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+          # Configurable; defaults to Sonnet for cost on an archive repo.
+          model: ${{ vars.AI_MODEL || 'claude-sonnet-4-6' }}

.github/workflows/docs.yml

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+name: Deploy docs (Cloudflare Pages)
+
+on:
+  push:
+    branches: [main, master]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: docs-deploy
+  cancel-in-progress: true
+
+jobs:
+  deploy:
+    name: Build & deploy to Cloudflare Pages
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install docs deps
+        run: pip install -r requirements-docs.txt
+
+      - name: Generate per-slug pages
+        run: python scripts/generate_progress.py --docs
+
+      - name: Build site
+        run: mkdocs build --strict
+
+      # Gated: only deploys when the Cloudflare secrets are configured. On forks
+      # / PRs without them this whole step is skipped, so the workflow stays
+      # green without ever needing a CF account during development.
+      - name: Check Cloudflare secrets
+        id: cf
+        run: |
+          if [ -n "${{ secrets.CLOUDFLARE_API_TOKEN }}" ] && [ -n "${{ secrets.CLOUDFLARE_ACCOUNT_ID }}" ]; then
+            echo "enabled=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "enabled=false" >> "$GITHUB_OUTPUT"
+            echo "::notice::Cloudflare secrets not set — skipping deploy (build verified only)."
+          fi
+
+      - name: Deploy to Cloudflare Pages
+        if: steps.cf.outputs.enabled == 'true'
+        uses: cloudflare/wrangler-action@v3
+        with:
+          apiToken: ${{ secrets.CLOUDFLARE_API_TOKEN }}
+          accountId: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}
+          command: pages deploy site --project-name=leetcode-problems

.gitignore

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+# mkdocs build output
+/site/
+
+# Generated docs pages (rebuilt by scripts/generate_progress.py --docs in CI;
+# not committed to avoid churn). Only docs/progress.json is committed so the
+# README's dynamic badges resolve without needing a docs build.
+/docs/problems/
+/docs/index.md
+/docs/tags.md
+/docs/lessons.md
+
+# Python
+__pycache__/
+*.pyc
+.venv/
+venv/
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Internal growth/marketing notes (not for public)
+GROWTH.md
+BANNER.md
+SUBMITTING_TO_AWESOME.md
+launch-kit.md
+star-strategy.md
+modernization-backlog.md

.pre-commit-config.yaml

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+# Mirrors the CI gates locally. Install: pip install pre-commit && pre-commit install
+repos:
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v5.0.0
+    hooks:
+      - id: end-of-file-fixer
+        exclude: '^solutions/'
+      - id: trailing-whitespace
+        exclude: '^solutions/'
+      - id: check-yaml
+
+  - repo: https://github.com/pre-commit/mirrors-clang-format
+    rev: v19.1.5
+    hooks:
+      - id: clang-format
+        files: '^solutions/.*Solution\.cpp$'
+
+  - repo: https://github.com/sqlfluff/sqlfluff
+    rev: 3.3.0
+    hooks:
+      - id: sqlfluff-lint
+        name: sqlfluff (oracle)
+        files: '\.oraclesql$'
+        args: ["--dialect", "oracle"]
+
+  - repo: local
+    hooks:
+      - id: progress-table
+        name: progress table up to date
+        entry: python scripts/generate_progress.py --check
+        language: system
+        pass_filenames: false
+        files: '^solutions/|^scripts/generate_progress\.py$'