题目链接
Hat’s Fibonacci HDU - 1250
题目
A Fibonacci sequence is calculated by adding the previous two members the sequence, with the first two members being both 1.
F(1) = 1, F(2) = 1, F(3) = 1,F(4) = 1, F(n>4) = F(n - 1) + F(n-2) + F(n-3) + F(n-4)
Your task is to take a number as input, and print that Fibonacci number.
Input
Each line will contain an integers. Process to end of file.
Output
For each case, output the result in a line.
Sample Input
100
Sample Output
4203968145672990846840663646
Note:
No generated Fibonacci number in excess of 2005 digits will be in the test data, ie. F(20) = 66526 has 5 digits.
题意
给定一个递推公式，要求求第n位的指。值的位数不超过2005位。
分析
递推，O(n)级别算法，时间肯定不会超限。
然后调用JAVA的BigInteger包来解决大数问题就好了。
AC代码
import java.math.BigInteger;
import java.util.Scanner;public class Main {public static void main(String[] args) {Scanner cin=new Scanner(System.in);int n;while(cin.hasNext()) {n=cin.nextInt();BigInteger a,b,c,d,e;a=BigInteger.ONE;b=c=d=e=a;for(int i=5;i<=n;i++) {e=a.add(b).add(c).add(d);a=b;b=c;c=d;d=e;}System.out.println(e);}}
}