[Java implements sword offer] Fibonacci sequence problem

Find the nth term of the Fibonacci sequence

• recursion

public int Fibonacci(int n){
    int[] result = {0,1};
    if(n<2)
        return result[n];
    return Fibonacci(n-1)+Fibonacci(n-2);

}

• non-recursive

public int Fibonacci(int n){
    int[] result = {0,1};
    if(n<2)
        return result[n];
    int sum = 0;
    int left = 0;
    int right = 1;
    for(int i=2;i<=n;i++){
        sum = left + right;
        left = right;
        right = sum;
    }
    return sum;
}

A frog can jump up 1 steps at a time, or 2 steps at a time. Find how many ways the frog can jump up a n-level stair.

Ideas:
If you jump 1 step for the first time, the remaining n-1; if you jump 2 steps, the remaining n-2;

A frog can jump up 1 steps at a time, it can jump up 2 steps...it can also jump up n steps. Find the total number of ways the frog can jump up a n steps

With the above foreshadowing, if you jump 1 step for the first time, there will be n-1 remaining; if you jump 2 steps for the first time, there will be n-2 remaining;
if you jump 3 steps for the first time, there will be n-3 remaining. . . .

$$f(n)=f(n-1)+f(n-2)+f(n-3)+...+f(1)$$
$$f(n-1)=f(n-2)+f(n-3)+...+f(1)$$
Subtract two formulas $f(n)=2*f(n-1)$

public class Solution {
    public int JumpFloorII(int target) {

        int[] result = {0,1};
        if(target<2)
            return result[target];
        int sum = 1;
        for(int i=2;i<=target;i++){
            sum *= 2;
        }
        return sum;
    }
}