feat: refactored docs structure

docs/(04-relational)/topological-sort/(problems)/207_course-schedule.mdx

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+---
+title: '207. Course Schedule'
+description: There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai, bi] indicates that you must take course bi first if you want to take course ai
+icon: dot
+topics:
+  - { name: "Depth-First Search", slug: "depth-first-search" }
+  - { name: "Breadth-First Search", slug: "breadth-first-search" }
+  - { name: "Graph Theory", slug: "graph" }
+  - { name: "Topological Sort", slug: "topological-sort" }
+  - { name: "Directed Acyclic Graph", slug: "directed-acyclic-graph" }
+issue: "https://github.com/prdlk/leetcode/issues/142"
+sidebar:
+  label: 'Course Schedule'
+  badge: 'Medium'
+---
+
+### Example 1:
+- Input: `numCourses = 2, prerequisites = [[1,0]]`
+- Output: `true`
+- Explanation: There are a total of `2` courses to take. To take course `1` you should have finished course `0`. So it is possible.
+
+### Example 2:
+- Input: `numCourses = 2, prerequisites = [[1,0],[0,1]]`
+- Output: `false`
+- Explanation: There are a total of `2` courses to take. To take course `1` you should have finished course `0`, and to take course `0` you should also have finished course `1`. So it is impossible.
+
+### Constraints:
+
+- `1 <= numCourses <= 2000`
+- `0 <= prerequisites.length <= 5000`
+- `prerequisites[i].length == 2`
+- `0 <= ai, bi < numCourses`
+- All the pairs `prerequisites[i]` are unique.
+
+## Solution
+
+```py
+class Solution:
+    def canFinish(self, numCourses: int, prerequisites: list[list[int]]) -> bool:
+        indegree = [0] * numCourses
+        adj = [[] for x in range(numCourses)]
+        for prereq in prerequisites:
+            adj[prereq[1]].append(prereq[0])
+            indegree[prereq[0]] += 1
+
+        queue = []
+
+        for i in range(numCourses):
+            if indegree[i] == 0:
+                queue.append(i)
+
+        visited = 0
+        while queue:
+            node = queue.pop(0)
+            visited += 1
+            for neighbor in adj[node]:
+                indegree[neighbor] -= 1
+                if indegree[neighbor] == 0:
+                    queue.append(neighbor)
+
+        return numCourses == visited
+```

docs/(04-relational)/topological-sort/(problems)/210_course-schedule-ii.mdx

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+---
+title: '210. Course Schedule II'
+description: There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai, bi] indicates that you must take course bi first if you want to take course ai
+icon: dot
+topics:
+  - { name: "Depth-First Search", slug: "depth-first-search" }
+  - { name: "Breadth-First Search", slug: "breadth-first-search" }
+  - { name: "Graph Theory", slug: "graph" }
+  - { name: "Topological Sort", slug: "topological-sort" }
+issue: "https://github.com/prdlk/leetcode/issues/143"
+sidebar:
+  label: 'Course Schedule II'
+  badge: 'Medium'
+---
+
+### Example 1:
+- Input: `numCourses = 2, prerequisites = [[1,0]]`
+- Output: `[0,1]`
+- Explanation: There are a total of `2` courses to take. To take course `1` you should have finished course `0`. So the correct course order is `[0,1]`.
+
+### Example 2:
+- Input: `numCourses = 4, prerequisites = [[1,0],[2,0],[3,1],[3,2]]`
+- Output: `[0,2,1,3]`
+- Explanation: There are a total of `4` courses to take. To take course `3` you should have finished both courses `1` and `2`. Both courses `1` and `2` should be taken after you finished course `0`. So one correct course order is `[0,1,2,3]`. Another correct ordering is `[0,2,1,3]`.
+
+### Example 3:
+- Input: `numCourses = 1, prerequisites = []`
+- Output: `[0]`
+
+### Constraints:
+
+- `1 <= numCourses <= 2000`
+- `0 <= prerequisites.length <= numCourses * (numCourses - 1)`
+- `prerequisites[i].length == 2`
+- `0 <= ai, bi < numCourses`
+- `ai != bi`
+- All the pairs [ai, bi] are distinct.
+
+## Solution
+
+```py
+class Solution:
+    def findOrder(self, numCourses: int, prerequisites: list[list[int]]) -> list[int]:
+        prereq = {c: [] for c in range(numCourses)}
+        for crs, pre in prerequisites:
+            prereq[crs].append(pre)
+
+        # course has 3 possible states:
+        # visited -> crs has been added to output
+        # visiting -> crs not added to output, but added to cycle
+        # unvisited -> crs not added to output nor cycle
+        output = []
+        visit, cycle = set(), set()
+
+        def dfs(crs):
+            if crs in cycle:
+                return False
+            if crs in visit:
+                return True
+
+            cycle.add(crs)
+            for pre in prereq[crs]:
+                if dfs(pre) == False:
+                    return False
+
+            cycle.remove(crs)
+            visit.add(crs)
+            output.append(crs)
+            return True
+
+        for c in range(numCourses):
+            if dfs(c) == False:
+                return []
+
+        return output
+```