5. Dynamic programming -- Fibonacci series

Title Description ：f(0) = 0, f(1) = 1,f(n) = f(n - 1) + f(n - 2), among n> 1. The answer needs to be modelled
     1e9+7（1000000007）

 public int fib(int n) {
        int a = 0, b = 1, sum;
        for(int i = 0; i < n; i++){
            sum = (a + b) % 1000000007;
            a = b;
            b = sum;
        }
        return a;
    }

Dynamic programming algorithm is

• For a scale of n The problem of , Break it down into k A smaller sub problem （ Stage ）, Solve the subproblems in order , The solution of the previous subproblem , It provides useful information for the solution of the latter subproblem . In solving any subproblem , The local optimal solution is obtained through decision-making , Solve each sub problem in turn . Finally, you can make a simple judgment , Get the solution of the original problem .