feat(content): add new patterns

backend/data/patterns/patterns.yaml

@@ -127,3 +127,53 @@ patterns:
       - Longest common prefix
       - Word break problems
       - Spell checker
+
+  - name: Prefix Sum
+    slug: prefix-sum
+    description: Precompute cumulative sums to answer range queries in O(1) time.
+    when_to_use: |
+      - Range sum queries
+      - Subarray sum equals target
+      - Product of array except self
+      - Count subarrays with given sum
+      - 2D matrix region sums
+
+  - name: LinkedList In-Place Reversal
+    slug: linkedlist-reversal
+    description: Reverse linked list nodes in-place by manipulating pointers without extra space.
+    when_to_use: |
+      - Reverse entire linked list
+      - Reverse a portion of linked list
+      - Reverse in groups of K
+      - Palindrome linked list check
+      - Reorder list problems
+
+  - name: Overlapping Intervals
+    slug: intervals
+    description: Process and merge intervals that share common ranges.
+    when_to_use: |
+      - Merge overlapping intervals
+      - Insert interval into sorted list
+      - Meeting rooms scheduling
+      - Find gaps between intervals
+      - Interval intersection problems
+
+  - name: Binary Tree Traversal
+    slug: tree-traversal
+    description: Visit tree nodes in specific orders - preorder, inorder, postorder, or level-order.
+    when_to_use: |
+      - Serialize/deserialize trees
+      - Validate BST (inorder)
+      - Copy or compare trees
+      - Path sum problems
+      - Tree construction from traversals
+
+  - name: Matrix Traversal
+    slug: matrix-traversal
+    description: Navigate 2D grids using DFS, BFS, or directional iteration.
+    when_to_use: |
+      - Number of islands / connected regions
+      - Shortest path in grid
+      - Flood fill
+      - Rotting oranges
+      - Word search in grid