斐波那契数列-递归层级是有限的，伪递归

public class Solution {
    public int Fib(int n) {
        if(n==0 || n ==1) return n;
        int[] cache = new int[n+1];
        cache[0] = 0;
        cache[1] = 1;
        for(int i=2;i<=n;i++)
        {
            cache[i] = (cache[i-1]+cache[i-2])%1000000007;
        }
        return cache[n];
    }

    public int FibCache(int n,int[] cache)
    {
        if(n == 0) return 0;
        if(n == 1) return 1;
        if(cache[n] != 0) return cache[n];
        cache[n] = Fib(n-1) + Fib(n-2);
        return cache[n] % 1000000007;
    }
}