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Merge pull request #2022 from codeflash-ai/codeflash/optimize-Fibonacci.fibonacci-mnqq81k5

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⚡️ Speed up method `Fibonacci.fibonacci` by 2,036%
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claude[bot] 2026-04-09 08:22:52 +00:00 committed by GitHub
commit 5ce36eddce
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1 changed files with 23 additions and 2 deletions
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code_to_optimize/java/src/main/java/com/example/Fibonacci.java
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@ -9,7 +9,7 @@ import java.util.List;
public class Fibonacci { public class Fibonacci {
/** /**
* Calculate the nth Fibonacci number using recursion. * Calculate the nth Fibonacci number using an efficient iterative fast-doubling algorithm.
* *
* @param n Position in Fibonacci sequence (0-indexed) * @param n Position in Fibonacci sequence (0-indexed)
* @return The nth Fibonacci number * @return The nth Fibonacci number
@ -21,7 +21,28 @@ public class Fibonacci {
if (n <= 1) { if (n <= 1) {
return n; return n;
} }
return fibonacci(n - 1) + fibonacci(n - 2);
long a = 0L; // F(0)
long b = 1L; // F(1)
// Iterate from the highest bit of n down to the lowest.
for (int mask = Integer.highestOneBit(n); mask != 0; mask >>= 1) {
// Apply doubling formulas:
// F(2k) = F(k) * (2*F(k+1) - F(k))
// F(2k+1) = F(k+1)^2 + F(k)^2
long twoBMinusA = (b << 1) - a;
long c = a * twoBMinusA; // F(2k)
long d = a * a + b * b; // F(2k+1)
if ((n & mask) == 0) {
a = c;
b = d;
} else {
a = d;
b = c + d;
}
}
return a;
} }
/** /**