f(1) = 1; f(2) = 1; f(3) = f(1) + f(2);以此内推1                           x = 1
f(x) = 1                           x = 2f(x - 1)  + f(x - 2)        x >= 3

#include <stdio.h>
#include <stdlib.h>int fib1(int n)
{if (n <= 0)return -1;else if (n == 1 || n == 2)return 1;elsereturn fib1(n - 1) + fib1(n - 2);
}int fib2(int n)
{if (n <= 0)return -1;int *a = malloc(sizeof(int) * n); //开辟了一个数组a[1] = 1;a[2] = 1;for (int i = 3; i <= n; ++i){a[i] = a[i - 1] + a[i - 2];}return a[n];
}int fib3(int n)
{if (n <= 0)return -1;int a1 = 1;