题目：

题解：

typedef struct Trie {struct Trie * children[26];bool isEnd;
}Trie;#define TRIE_INITIAL(node) do { \for (int i = 0; i < 26; ++i) { \(node)->children[i] = NULL; \} \(node)->isEnd = false; \
}while(0);static void freeTrie(Trie * node) {if (NULL == node) {return;}for (int i = 0; i < 26; ++i) {if (node->children[i] != NULL) {freeTrie(node->children[i]);}}free(node);
}static int cmp(const void * pa, const void * pb){int la = strlen(*(char **)pa);int lb = strlen(*(char **)pb);return la - lb;
}bool dfs(Trie * trie, const char * word, int wordSize, int start, int* visited) {if (wordSize == start) {return true;}if (visited[start]) {return false;}visited[start] = 1;Trie * node = trie;for (int i = start; i < wordSize; i++) {char ch = word[i];int index = ch - 'a';node = node->children[index];if (node == NULL) {return false;}if (node->isEnd) {if (dfs(trie, word, wordSize, i + 1, visited)) {return true;}}}return false;
}void insert(Trie * trie, const char * word, int wordSize) {Trie * node = trie;for (int i = 0; i < wordSize; i++) {char ch = word[i];int index = ch - 'a';if (node->children[index] == NULL) {node->children[index] = (Trie *)malloc(sizeof(Trie));TRIE_INITIAL(node->children[index]);}node = node->children[index];}node->isEnd = true;
}char ** findAllConcatenatedWordsInADict(char ** words, int wordsSize, int* returnSize){    int pos = 0;char ** ans = (char **)malloc(sizeof(char *) * wordsSize);Trie * trie = (Trie *)malloc(sizeof(Trie));TRIE_INITIAL(trie);qsort(words, wordsSize, sizeof(char *), cmp);for (int i = 0; i < wordsSize; i++) {int len = strlen(words[i]);if (len == 0) {continue;}int * visited = (int *)malloc(sizeof(int) * len);memset(visited, 0, sizeof(int) * len);if (dfs(trie, words[i], len, 0, visited)) {ans[pos] = (char *)malloc(sizeof(char) * (len + 1));strncpy(ans[pos], words[i], len);ans[pos][len] = '\0';pos++;} else {insert(trie, words[i], len);}free(visited);}freeTrie(trie);*returnSize = pos;return ans;
}