已知斐波納契數列如下:F[1] = 1, F[2] = 1, F[3] = 2, F[4] = 3, ..., F[n] = F[n-1] + F[n-2],那麼請問F[34] + F[32] == ?
解題思路:運用HashMap存儲已經計算過的斐波那契數,這樣可以大量減少重複的計算。
import java.util.HashMap;
import java.util.Map;
public class Fibonacci {
private Map<Integer, Long> map;
public Fibonacci() {
map = new HashMap<Integer, Long>();
map.put(1, Long.valueOf(1));
map.put(2, Long.valueOf(1));
}
long fibonacci(int n) {
assert(n > 0);
if(map.containsKey(n))
return map.get(n).longValue();
long fn = fibonacci(n - 1) + fibonacci(n - 2);
map.put(n, Long.valueOf(fn));
return fn;
}
public static void main(String[] args) {
Fibonacci fibonacci = new Fibonacci();
System.out.println(
String.format("F[34] + F[32] = %d",
fibonacci.fibonacci(34) + fibonacci.fibonacci(32)));
}
}