FlipGameII.java

import java.util.HashMap;
import java.util.Map;

public class FlipGameII {
 /**
 AmazonDebug 1:
 Recursion
 T(N) = (N - 1) * T(N - 2) = (N - 1) * (N - 3) * T(N - 4) = (N - 1) !

 canWin("++++++") = !canWin("--++++") || !canWin("+--+++") || !canWin("++--++") || !canWin("+++--+") || !canWin("++++--")

 AmazonDebug 2:
 Recursion + memoriztion

 */




 public boolean canWin(String s) {

 return canWinHelper(s.toCharArray(), new HashMap<>());
 }

 public boolean canWinHelper(char[] chars, Map<char[], Boolean> map) {
 if(map.get(chars) != null) {
 return map.get(chars);
 }

 boolean res = false;
 for(int i = 0; i < chars.length - 1; i++) {
 if(chars[i] == '+' && chars[i + 1] =='+') {
 chars[i] = '-';
 chars[i + 1] = '-';
 res = res || !canWinHelper(chars, map);
 chars[i] = '+';
 chars[i + 1] = '+';
 }

 }
 map.put(chars.clone(), res);
 return res;
 }

 public static void main(String[] args) {
 String input = "++++";
 FlipGameII a = new FlipGameII();
 a.canWin(input);
 }
}