You keep reassign a new value to easyPuzzle when you really want to concatenate:
easyPuzzle += easy[i].toString();
If easy.length is large, it might make sense to use a StringBuilder which is more efficient at concatenating than String:
StringBuilder builder = new StringBuilder();
for(int i=1; i < easy.length; i++){
builder.append(easy[i].toString());
}
easyPuzzle = builder.toString();
Also by starting your for loop at i=1 you exclude the first item. Not sure if it is on purpose or not. If not, start at i = 0.
Alternatively, to save the pain of writing the loop yourself, you can use @Manoj's answer which replaces your code by one line.