无穷数列1,1,2,3,5,8,13,21,34,55,…,被称为Fibonacci数列。
1.解法:使用一个数组来记录各个子问题的解(自顶向下),数组最开始要初始化为0.
public class Fibonacci {
static ArrayList<Integer> list=new ArrayList<Integer>();
public static void main(String[] args) {
Integer N = 3;
list.add(1);
list.add(1);
int length = N-list.size();
for (int i = 0; i < length; i++) {
list.add(0);
}
System.out.println(list);
System.out.println(fibonacci(N));
System.out.println(list);
}
private static int fibonacci(int n) {
if(list.get(n-1)!=0){
return list.get(n-1);
}
list.set(n-1,fibonacci(n-1)+fibonacci(n-2));
return list.get(n-1);
}
}
2.采用自底向上的方法:
public class Fibonacci {
static ArrayList<Integer> list=new ArrayList<Integer>();
public static void main(String[] args) {
Integer N = 10;
list.add(1);
list.add(1);
System.out.println(list);
System.out.println(fibonacci_2(N));
System.out.println(list);
}
private static int fibonacci_2(Integer n) {
for (int i = 2; i <= n; i++) {
list.add(i,list.get(i-2)+list.get(i-1));
}
return list.get(n);
}