Fibonacciアルゴリズムの3つの実装と性能の比較
コードは次のとおりです.
テスト結果:
再帰アルゴリズムを削除し、テストします. Recursiveアルゴリズムは自身を呼び出し続けるため、深さ計算が多すぎて、性能が非常に低下し、n>=50の場合、Recursiveアルゴリズムにかかる時間はもう我慢できない. CacheアルゴリズムとSwapアルゴリズムはwhileサイクルで絶えず計算と更新されているだけで、Cacheアルゴリズムは毎回計算値をリストに保存し、消費メモリが多すぎて、性能もSwapの良いものではありません.
import java.util.ArrayList;
import java.util.List;
public class Fibonacci {
/**
* ：
* @param n
* @return
*/
public static Long recursiveCompute(int n) {
if (n <= 2)
return 1L;
else
return recursiveCompute(n - 1) + recursiveCompute(n - 2);
}
/**
* cache ： List 1~n Fibonacci
* @param n
* @return
*/
public static Long cacheCompute(int n) {
if (n <= 2)
return 1L;
List<Long> results = new ArrayList<Long>();
results.add(1L);
results.add(1L);
int length = -1;
while ((length = results.size()) < n)
results.add(results.get(length - 2) + results.get(length - 1));
return results.get(n - 1);
}
/**
* swap ： l1、l2 Fibonacci ， update swap
* @param n
* @return
*/
public static Long swapCompute(int n) {
if (n <= 2)
return 1L;
long l1 = 1;
long l2 = 1;
int index = 2;
while (index < n - 1) {
long l = l2;
l2 = l1 + l2;
l1 = l;
index++;
}
return l1 + l2;
}
public static void testTime(int n) {
Long result = 0L;
long start = System.nanoTime();
result = recursiveCompute(n);
long end = System.nanoTime();
System.out.println("Recursive Compute: " + result + "\tUse Time: " + (end - start));
start = System.nanoTime();
result = cacheCompute(n);
end = System.nanoTime();
System.out.println("Cache Compute: " + result + "\tUse Time: " + (end - start));
start = System.nanoTime();
result = swapCompute(n);
end = System.nanoTime();
System.out.println("Swap Compute: " + result + "\tUse Time: " + (end - start));
}
public static void main(String[] args) {
System.out.println("Compute Fibonacci(10):");
testTime(10);
System.out.println("
Compute Fibonacci(20):");
testTime(20);
System.out.println("
Compute Fibonacci(30):");
testTime(30);
System.out.println("
Compute Fibonacci(40):");
testTime(40);
System.out.println("
Compute Fibonacci(50):");
testTime(50);
}
}テスト結果:
Compute Fibonacci(10):
Recursive Compute: 55 Use Time: 26944
Cache Compute: 55 Use Time: 52444
Swap Compute: 55 Use Time: 4330
Compute Fibonacci(20):
Recursive Compute: 6765 Use Time: 1528093
Cache Compute: 6765 Use Time: 26463
Swap Compute: 6765 Use Time: 1443
Compute Fibonacci(30):
Recursive Compute: 832040 Use Time: 17896390
Cache Compute: 832040 Use Time: 48595
Swap Compute: 832040 Use Time: 1924
Compute Fibonacci(40):
Recursive Compute: 102334155 Use Time: 2385636507
Cache Compute: 102334155 Use Time: 54850
Swap Compute: 102334155 Use Time: 1924
Compute Fibonacci(50):
Recursive Compute: 12586269025 Use Time: 287928822445
Cache Compute: 12586269025 Use Time: 76501
Swap Compute: 12586269025 Use Time: 2887再帰アルゴリズムを削除し、テストします.
Compute Fibonacci(100):
Cache Compute: 3736710778780434371 Use Time: 274730
Swap Compute: 3736710778780434371 Use Time: 10104
Compute Fibonacci(1000):
Cache Compute: 817770325994397771 Use Time: 1330826
Swap Compute: 817770325994397771 Use Time: 44746
Compute Fibonacci(10000):
Cache Compute: -2872092127636481573 Use Time: 4596307
Swap Compute: -2872092127636481573 Use Time: 326211
Compute Fibonacci(50000):
Cache Compute: -806788626697678875 Use Time: 14161801
Swap Compute: -806788626697678875 Use Time: 1218240