https://leetcode.com/problems/frog-jump/// 受以下网页启发，用递归可行// https://discuss.leetcode.com/topic/59337/easy-version-javapublic class Solution {    Map mp;    private int[] stones;    public boolean canCross(int[] s) {        stones = s;                if (stones[1] != 1) {            return false;        }        if (stones.length < 3) {            return true;        }        mp = new HashMap();        Set st = new HashSet();        st.add(1);        mp.put(1, st);        for (int i=2; i
     
      = step - 1 && dist <= step + 1) {                if (impl(i, dist)) {                    return true;                }            }        }        return false;    }}*/