Recursion vs Iteration
Many problems can be solved both recursively and iteratively (using loops). Which one should you choose? Both have trade-offs.
Recursion
- Pros: Code is often shorter, more elegant, matches mathematical definition.
- Cons: Uses more memory (call stack), may be slower, risk of stack overflow for deep recursion.
Iteration (Loops)
- Pros: Usually faster, uses constant memory (no stack), no overflow risk.
- Cons: Code can be more complex, especially for tree/graph algorithms.
Example: Fibonacci numbers
// Recursive (exponential time, O(2^n))
static int fibRecursive(int n) {
if (n <= 1) return n;
return fibRecursive(n-1) + fibRecursive(n-2);
}
// Iterative (linear time, O(n))
static int fibIterative(int n) {
if (n <= 1) return n;
int prev2 = 0, prev1 = 1, current = 0;
for (int i = 2; i <= n; i++) {
current = prev1 + prev2;
prev2 = prev1;
prev1 = current;
}
return current;
}
In practice, choose recursion for problems with a natural recursive structure (trees, backtracking) and iteration for performance-critical tasks.
Two Minute Drill
- Recursion: concise, natural for divide-and-conquer, but uses stack memory.
- Iteration: faster, constant memory, but can be more complex.
- Tail recursion can be optimized by some compilers, but Java doesn't guarantee it.
- Choose based on problem nature and constraints.
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