509. Fibonacci Number

The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,

>F(0) = 0, F(1) = 1
>F(n) = F(n - 1) + F(n - 2), for n > 1.

Given n, calculate F(n).

class Solution {
    int dp[31] = {0,};
public:
    int fib(int n) {
        if(n <= 1) return n;
        if(dp[n]) return dp[n];
        return dp[n] = fib(n-1) + fib(n-2);
    }
};