Fundamentals · Medium · Free
Draw a recursion tree for merge sort or Fibonacci — why it matters.
FresherFundamentalsData Structures & Algorithms
Recursion tree
Draw calls as tree nodes—leaves count × work per call estimates complexity (e.g., merge sort levels × merge cost).
diagram
mergeSort(n)
├── n/2
└── n/2 → log n levels, n work/level → O(n log n)java
int naiveFib(int n) {
if (n <= 1) return n;
return naiveFib(n - 1) + naiveFib(n - 2); // tree ~ 2^n calls
}Fibonacci naive tree is bushy—explains exponential time.