斐波那契数列 1,1,2,3,5,8,13,21....
通项公式 fib(n) = fib(n-1) + fib(n-2)
- 普通迭代
...
- 普通递归
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private static long fib(int n){
return n<=2?1:(fib(n-1)+fib(n-2));
}
- 带缓存的递归
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static Map<Integer,Long> cache2 = new HashMap<>();
private static long fib2(int n){
if(n <= 2) return 1L;
if(cache2.containsKey(n))
return cache2.get(n);
Long fibn = fib2(n-1)+fib2(n-2);
cache2.put(n, fibn);
return fibn;
}
- 使用 BigInteger 防止溢出
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static Map<Integer, BigInteger> cache = new HashMap<>();
public static void main(String[] args) {
int n = 100;
BigInteger bi = fib(n);
System.out.println(bi);
}
private static BigInteger fib(int n) {
if(n <= 2) return BigInteger.ONE;
if(cache.containsKey(n))
return cache.get(n);
BigInteger t = new BigInteger(fib(n-1).toByteArray()).
add(new BigInteger(fib(n-2).toByteArray()));
cache.put(n, t);
return t;
}
- 斐波那契数列迭代器
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/**
* 定义一个遍历器，用于遍历斐波那契数字。
*
* @author moveb
*
*/
public class T24_13_FibonacciIterator implements Iterator<Integer> {
private int upBound = 23302;
private int pre = 1;
private int cur = 1;
public T24_13_FibonacciIterator(){}
public T24_13_FibonacciIterator(int ub){
upBound = ub;
}
@Override
public boolean hasNext() {
return (cur < upBound);
}
@Override
public Integer next() {
int fib = cur;
cur = cur + pre;
pre = fib;
return fib;
}
@Override
public void remove() {
}
}
