[动态规划] leetcode 1048 Longest String Chain

problem:https://leetcode.com/problems/longest-string-chain/

        爬台阶类型问题。从长度为k转换为长度为k + 1的字符串。此处通过删掉一个字符，查看删掉后的字符串是否存在来判断能否转换。

bool cmp(const string &s1, const string &s2) {
    return s1.size() == s2.size() ? s1 < s2 : s1.size() < s2.size();
}
class Solution {
public:
    int longestStrChain(vector<string>& words) {
        vector<int> dp(words.size(), 1);
        map<string, int, function<bool(const string &, const string &)>> mapWord(cmp);
        
        for (int i = 0;i<words.size();i++)
        {
            mapWord[words[i]] = i;
        }
        int result = 1;
        int i = 0;
        for (auto it = mapWord.begin();it != mapWord.end();it++)
        {
            string word = it->first;
            it->second = i;
            //cout << word << endl;
            for (int j = 0;j<word.size();j++)
            {
                string subWord = word.substr(0, j) + word.substr(j + 1, word.size() - j);
                if (mapWord.find(subWord) != mapWord.end())
                {
                    int idx = mapWord[subWord];
                    dp[i] = max(dp[i], dp[idx] + 1);
                }
            }
            if (dp[i] > result) result = dp[i];
            i++;
        }
        return result;
    }
};