Leetcode-392 Is Subsequence(判断子序列)

class Solution
{
    public:
        bool isSubsequence(string s, string t)
        {
            vector<int> WordList[26];
            for(int i = 0;i < t.size();i ++)
            {
                WordList[t[i]-'a'].emplace_back(i);
            }
            
            int pre_index = 0;
            for(int i = 0;i < s.size();i ++)
            {
                auto v_ptr = lower_bound(WordList[s[i]-'a'].begin(),WordList[s[i]-'a'].end(),pre_index);
                if(v_ptr == WordList[s[i]-'a'].end())
                    return false;
                pre_index = *v_ptr+1;
            }
            return true;
        }
};