import java.util.*;
public class FrogJumpTopicDP {

    public boolean canCross(int[] stones) { Map<Integer, Set<Integer>> map = new HashMap<>();
        for (int s : stones) map.put(s, new HashSet<>());
        map.get(0).add(0);
        for (int s : stones) for (int k : map.get(s)) for (int step = k - 1;
        step <= k + 1;
        step++) if (step > 0 && map.containsKey(s + step)) map.get(s + step).add(step);
        return !map.get(stones[stones.length - 1]).isEmpty();
    };
}