week 6 292. Nim Game

public class Solution {
    public boolean canWinNim(int n) {
        return helper(n, new HashMap<>());
    }
    
    public boolean helper (int n, Map<Integer, Boolean> map){
        if(n <= 0){
            return false;
        }
        if(map.containsKey(n)){
            return map.get(n);
        }
        boolean canNextWin = true;
        for(int i = 1; i <= 3; i++){
            canNextWin &= helper(n - i, map);
        }
        map.put(n, !canNextWin);
        return !canNextWin;
        
    }
}