0472-concatenated-words.cpp

/*
class Solution {
public:
    vector<string> findAllConcatenatedWordsInADict(vector<string>& words) {
        unordered_set<string> bag(words.begin(), words.end());
        vector<string> res;
        for (auto word: words) {
            string subWord = "";
            int count = 0;
            for (int i = word.size() - 1; i >= 0; i--) {
                subWord = word[i] + subWord;
                if (bag.count(subWord)) {
                    count++;
                    subWord = "";
                }
            }
            if (subWord.size() == 0 && count >= 2) res.push_back(word);
        }
        return res;
    }
};
*/

class Solution {
public:
    vector<string> findAllConcatenatedWordsInADict(vector<string>& words) {
        unordered_set<string> dictionary(words.begin(), words.end());
        vector<string> answer;
        
        for (const string& word : words) {
            const int length = word.size();
            vector<bool> dp(length + 1); dp[0] = true;
            
            for (int i = 1; i <= length; ++i)
                for (int j = i == length; !dp[i] && j < i; ++j)
                    dp[i] = dp[j] && dictionary.count(word.substr(j, i - j));
            
            if (dp[length]) answer.push_back(word);
        }
        return answer;
    }
};