# Graphs — Problem Tracker

[অধ্যায়ে ফিরুন](../README.md) · [সহজ ব্যাখ্যা ও ব্যবহার](../learning-guide.md) · [উৎসের তালিকা](../source-map.md)

> **লিংক পড়ার নিয়ম:** Source খুললে প্ল্যাটফর্মের মূল প্রশ্ন, Note file খুললে এই সাইটের ব্যাখ্যা ও সমাধান পাবেন। নোটগুলো আগে থেকেই লেখা আছে। `planned` হলো আপনার ব্যক্তিগত অনুশীলনের অবস্থা, নোট অনুপস্থিত থাকার চিহ্ন নয়। প্ল্যাটফর্মের কিছু প্রশ্নে লগইন বা Premium লাগতে পারে; স্থানীয় নোট সরাসরি পড়া যাবে।

এই folder টা graphs-এর practice problem গুলো track করে। প্রতিটা problem-এর জন্য নিজের একটা note file থাকবে (**Note file** column-এ নাম দেওয়া), যেটা [../../templates/ds-problem-note-template.md](../../templates/ds-problem-note-template.md)-এর 24-section template দিয়ে লেখা — analogy, pattern, thinking tweak, dry run, complexity, mistakes, আর বাকি সব। List টা easy থেকে hard-এ সাজানো আর এমনভাবে group করা যাতে mixing শুরুর আগে প্রতিটা algorithm (BFS → DFS → topo sort → Dijkstra) একগুচ্ছ করে problem পায়।

এই tracker কীভাবে ব্যবহার করবে:

1. Link দিয়ে official statement টা পড়ো (মূল [../README.md](../README.md)-এর practice list-এও আছে)।
2. Code করার আগে জোরে বলো: *আমার nodes কী, edges কী, কোন algorithm আর কেন।* এই modeling বাক্যটাই পুরো repo-র সবচেয়ে interview-মূল্যবান অভ্যাস।
3. কিছু দেখার আগে অন্তত 25 মিনিট attempt করো।
4. Note file টা বানাও, template ভরো, Status-কে `solved` করো (বা `revisit`)।

Status values: `planned` → `attempted` → `solved` / `revisit`।

## Tracker

| # | Problem | Difficulty | Source | Pattern | Inherits from | Note file | Status |
| --- | --- | --- | --- | --- | --- | --- | --- |
| 1 | Find Center of Star Graph | Easy | [LeetCode 1791](https://leetcode.com/problems/find-center-of-star-graph/) | Representation warm-up | `09` adjacency basics | [001-find-center-of-star-graph.md](001-find-center-of-star-graph.md) | planned |
| 2 | Find if Path Exists in Graph | Easy | [LeetCode 1971](https://leetcode.com/problems/find-if-path-exists-in-graph/) | Reachability | `04-stack-and-queue` queue | [002-find-if-path-exists.md](002-find-if-path-exists.md) | planned |
| 3 | Flood Fill | Easy | [LeetCode 733](https://leetcode.com/problems/flood-fill/) | DFS on grid | `06-recursion-and-backtracking` | [003-flood-fill.md](003-flood-fill.md) | planned |
| 4 | Number of Islands | Medium | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) | Components on grid | `09` flood fill (#3) | [004-number-of-islands.md](004-number-of-islands.md) | planned |
| 5 | Max Area of Island | Medium | [LeetCode 695](https://leetcode.com/problems/max-area-of-island/) | Components + size counting | `09` islands (#4) | [005-max-area-of-island.md](005-max-area-of-island.md) | planned |
| 6 | Number of Provinces | Medium | [LeetCode 547](https://leetcode.com/problems/number-of-provinces/) | Components (matrix input) | `09` components; পরে আবার করো `10-disjoint-set-union` দিয়ে | [006-number-of-provinces.md](006-number-of-provinces.md) | planned |
| 7 | Building Roads | Easy | [CSES task 1666](https://cses.fi/problemset/task/1666) | Components, CP scale | `09` components | [007-building-roads.md](007-building-roads.md) | planned |
| 8 | Rotting Oranges | Medium | [LeetCode 994](https://leetcode.com/problems/rotting-oranges/) | Multi-source BFS | `04-stack-and-queue` queue | [008-rotting-oranges.md](008-rotting-oranges.md) | planned |
| 9 | 01 Matrix | Medium | [LeetCode 542](https://leetcode.com/problems/01-matrix/) | Multi-source BFS | `09` rotting oranges (#8) | [009-01-matrix.md](009-01-matrix.md) | planned |
| 10 | Labyrinth | Medium | [CSES task 1193](https://cses.fi/problemset/task/1193) | Grid BFS + path reconstruction | `09` BFS levels | [010-labyrinth.md](010-labyrinth.md) | planned |
| 11 | Is Graph Bipartite? | Medium | [LeetCode 785](https://leetcode.com/problems/is-graph-bipartite/) | BFS/DFS two-coloring | `09` BFS levels | [011-is-graph-bipartite.md](011-is-graph-bipartite.md) | planned |
| 12 | Building Teams | Medium | [CSES task 1668](https://cses.fi/problemset/task/1668) | Bipartite coloring, CP scale | `09` bipartite (#11) | [012-building-teams.md](012-building-teams.md) | planned |
| 13 | Clone Graph | Medium | [LeetCode 133](https://leetcode.com/problems/clone-graph/) | Traversal + copy map | `05-hashing` maps | [013-clone-graph.md](013-clone-graph.md) | planned |
| 14 | Pacific Atlantic Water Flow | Medium | [LeetCode 417](https://leetcode.com/problems/pacific-atlantic-water-flow/) | Reverse flood from borders | `09` flood fill (#3) | [014-pacific-atlantic.md](014-pacific-atlantic.md) | planned |
| 15 | Course Schedule | Medium | [LeetCode 207](https://leetcode.com/problems/course-schedule/) | Cycle detection (directed) | `06-recursion-and-backtracking` | [015-course-schedule.md](015-course-schedule.md) | planned |
| 16 | Course Schedule II | Medium | [LeetCode 210](https://leetcode.com/problems/course-schedule-ii/) | Topological sort (Kahn) | `09` course schedule (#15) | [016-course-schedule-ii.md](016-course-schedule-ii.md) | planned |
| 17 | Course Schedule (CSES) | Medium | [CSES task 1679](https://cses.fi/problemset/task/1679) | Topo sort, CP scale | `09` Kahn (#16) | [017-course-schedule-cses.md](017-course-schedule-cses.md) | planned |
| 18 | Network Delay Time | Medium | [LeetCode 743](https://leetcode.com/problems/network-delay-time/) | Dijkstra | `08-heap-priority-queue` heap | [018-network-delay-time.md](018-network-delay-time.md) | planned |
| 19 | Shortest Routes I | Medium | [CSES task 1671](https://cses.fi/problemset/task/1671) | Dijkstra, CP scale | `09` Dijkstra (#18) | [019-shortest-routes-i.md](019-shortest-routes-i.md) | planned |
| 20 | Path With Minimum Effort | Medium | [LeetCode 1631](https://leetcode.com/problems/path-with-minimum-effort/) | Minimax Dijkstra on grid | `09` Dijkstra (#18) | [020-path-with-minimum-effort.md](020-path-with-minimum-effort.md) | planned |
| 21 | Word Ladder | Hard | [LeetCode 127](https://leetcode.com/problems/word-ladder/) | BFS on implicit graph | `09` BFS + `05-hashing` | [021-word-ladder.md](021-word-ladder.md) | planned |
| 22 | Cheapest Flights Within K Stops | Hard | [LeetCode 787](https://leetcode.com/problems/cheapest-flights-within-k-stops/) | Bellman-Ford passes | `09` shortest-path table | [022-cheapest-flights-k-stops.md](022-cheapest-flights-k-stops.md) | planned |
| 23 | Bus Routes | Hard | [LeetCode 815](https://leetcode.com/problems/bus-routes/) | BFS on transformed graph | `09` modeling habit | [023-bus-routes.md](023-bus-routes.md) | planned |
| 24 | Alien Dictionary | Hard | [LeetCode 269](https://leetcode.com/problems/alien-dictionary/) | Build constraints + topo sort | `09` Kahn (#16) | [024-alien-dictionary.md](024-alien-dictionary.md) | planned |
| 25 | Swim in Rising Water | Hard | [LeetCode 778](https://leetcode.com/problems/swim-in-rising-water/) | Minimax Dijkstra | `09` minimax (#20); পরে আবার করো `10-disjoint-set-union` দিয়ে | [025-swim-in-rising-water.md](025-swim-in-rising-water.md) | planned |

## Suggested milestones (পরামর্শমতো মাইলফলক)

- #7-এর পর: components আর flood fill reflex হয়ে গেছে; না ভেবেই grid ↔ graph convert করতে পারো।
- #14-এর পর: BFS layers, multi-source seeding, আর reverse flooding — সব মিলে একটাই tool মনে হয়।
- #17-এর পর: directed graph-এ cycle detect আর ordering produce — দুটোই ঠান্ডা মাথায় পারো।
- #20-এর পর: Dijkstra plus তার minimax variant — "queue → deque → heap" বলো আর সত্যিই বোঝাও।
- #25-এর পর: অদ্ভুত statements-কে (buses, alien letters, rising water) graph হিসেবে model করতে পারো। এগিয়ে যাও [../../10-disjoint-set-union/](../../10-disjoint-set-union/README.md)-এ, তারপর #6 আর #25-এ ফিরে এসে DSU দিয়ে দ্বিতীয় solution লেখো — দুই solution-এর তুলনাতেই সবচেয়ে গভীর শেখাটা লুকিয়ে আছে।