Java find nth Fibonacci number example 2017-12-28 11:51
There are two ways to find nth Fibonacci number: recursion and loop. Recursion is easy to write but is inefficient. Loop is not easy to write but efficient.
Recursion(Not recommend)
public class FibonacciByRecursionClient {
public static void main(String[] args) {
System.out.println(getFibonacci(4));
}
private static int getFibonacci(int index) {
if (index <= 0) {
return -1;
}
if (index == 1 || index == 2) {
return 1;
}
return getFibonacci(index - 2) + getFibonacci(index - 1);
}
}
Loop
public class FibonacciByLoopClient {
public static void main(String[] args) {
System.out.println(getFibonacci(17));
}
public static int getFibonacci(int index) {
if (index <= 0) {
return -1;
}
if (index == 1 || index == 2) {
return 1;
}
//1 1 2 3 5 8 13 21 34 55
//1 2 3 4 5 6 7 8 9 10
int a = 1;
int b = 1;
int c = 0;
for (int i = 2; i < index; i++) {
c = a + b;
if (i == index - 1) {
break;
}
a = b;
b = c;
}
return c;
}
}
Summary
Get nth Fibonacci number in loop is not very difficult. Define b as preview number, a as the preview of b and c as the nth Fibonacci. After every loop moving a and b to next number.
EOF