December is the quiet before the storm. Use this time to tackle the topics you skipped. Here is a 15-day roadmap.
Days 1-5: Recursion & Backtracking
Solve N-Queens and Sudoku Solver. Understanding the flow of recursion is key to solving Trees and Graph problems later.
Days 6-10: Graphs (BFS/DFS)
Don't memorize code. Understand when to use BFS (shortest path) vs DFS (exploring paths). Solve 'Number of Islands' and 'Rotting Oranges'.
Days 11-15: Dynamic Programming
Start with 1D DP (Climbing Stairs). Move to Knapsack pattern. The trick to DP is not math; it is identifying the sub-problem. Draw the state transitions on paper before coding.