Recursion + Memorized Search(DP). And apparently, the code below can be iterative with only 3 vars - DP.

class Solution {    unordered_map
     
       cache;public:    bool go(int n)    {        if (n <=0) return false;        if (n < 3) return true;        if(cache.find(n) == cache.end())        {            cache[n] = !go(n - 1) || !go(n - 2);        }        return cache[n];    }    /**     * @param n: an integer     * @return: a boolean which equals to true if the first player will win     */     bool firstWillWin(int n) {        return go(n);    }};