题目：

题解：

char* id2str[26 * 26 * 26];int str2id(char* a) {int ret = 0;for (int i = 0; i < 3; i++) {ret = ret * 26 + a[i] - 'A';}return ret;
}int cmp(const void* _a, const void* _b) {int **a = (int**)_a, **b = (int**)_b;return (*b)[0] - (*a)[0] ? (*b)[0] - (*a)[0] : (*b)[1] - (*a)[1];
}int* vec[26 * 26 * 26];
int vec_len[26 * 26 * 26];
int* stk;
int stk_len;void dfs(int curr) {while (vec_len[curr] > 0) {int tmp = vec[curr][--vec_len[curr]];dfs(tmp);}stk[stk_len++] = curr;
}char** findItinerary(char*** tickets, int ticketsSize, int* ticketsColSize, int* returnSize) {memset(vec_len, 0, sizeof(vec_len));stk = malloc(sizeof(int) * (ticketsSize + 1));stk_len = 0;int* tickets_tmp[ticketsSize];for (int i = 0; i < ticketsSize; i++) {tickets_tmp[i] = (int*)malloc(sizeof(int) * 2);tickets_tmp[i][0] = str2id(tickets[i][0]);tickets_tmp[i][1] = str2id(tickets[i][1]);id2str[tickets_tmp[i][0]] = tickets[i][0];id2str[tickets_tmp[i][1]] = tickets[i][1];}qsort(tickets_tmp, ticketsSize, sizeof(int*), cmp);int add = 0;while (add < ticketsSize) {int adds = add + 1, start = tickets_tmp[add][0];while (adds < ticketsSize && start == tickets_tmp[adds][0]) {adds++;}vec_len[start] = adds - add;vec[start] = malloc(sizeof(int) * vec_len[start]);for (int i = add; i < adds; i++) {vec[start][i - add] = tickets_tmp[i][1];}add = adds;}dfs(str2id("JFK"));*returnSize = ticketsSize + 1;char** ret = malloc(sizeof(char*) * (ticketsSize + 1));for (int i = 0; i <= ticketsSize; i++) {ret[ticketsSize - i] = id2str[stk[i]];}return ret;
}