这道题对我来说开始没有思路，主要是没有抽象出来删除字符变为target应该如何简单实现？
看了一眼讨论区代码，知道如何实现后，又卡在了判断条件处，先根据长度简单判断，最后更新结果时判断能否通过删除字符得到target.

class Solution {
public:
    string findLongestWord(string s, vector<string>& d) {
        string res;
        for(int i = 0;i < d.size();i++)
        {
            
            if(d[i].size() >res.size() ||
              (d[i].size() == res.size() && d[i].compare(res) < 0)
              )
            {
                if(isSubstr(s,d[i]))
                    res = d[i];
            }
        }
        
        return res;
    }
private:
    //判断s能否通过删除字符得到target
    bool isSubstr(string s, string target) {
        int i = 0,j = 0;
        int size = target.size();
        
        while(i < s.size() && j < target.size())
        {
            if(s[i] == target[j])
                j++;
            i++;
        }
        
        return j == target.size();
    }
};

运行结果:

Runtime: 68 ms, faster than 69.34% of C++ online submissions for Longest Word in Dictionary through Deleting.
Memory Usage: 22.5 MB, less than 32.81% of C++ online submissions for Longest Word in Dictionary through Deleting.