题目：

题解：

struct Trie {int ch[27];int val;
} trie[50001];int size, nodeNum;void insert(char* s, int num) {int sSize = strlen(s), add = 0;for (int i = 0; i < sSize; ++i) {int x = s[i] - '`';if (trie[add].ch[x] == 0) {trie[add].ch[x] = ++size;memset(trie[size].ch, 0, sizeof(trie[size].ch));trie[size].val = -1;}add = trie[add].ch[x];}trie[add].val = num;
}int find(char* s) {int sSize = strlen(s), add = 0;for (int i = 0; i < sSize; ++i) {int x = s[i] - '`';if (trie[add].ch[x] == 0) {return -1;}add = trie[add].ch[x];}return trie[add].val;
}int addWord(char* word) {if (find(word) == -1) {insert(word, nodeNum++);}return find(word);
}int edge[30001][26];int edgeSize[30001];void addEdge(char* word) {int wordSize = strlen(word), id1 = addWord(word);for (int i = 0; i < wordSize; ++i) {char tmp = word[i];word[i] = '`';int id2 = addWord(word);edge[id1][edgeSize[id1]++] = id2;edge[id2][edgeSize[id2]++] = id1;word[i] = tmp;}
}int ladderLength(char* beginWord, char* endWord, char** wordList, int wordListSize) {size = nodeNum = 0;memset(trie[size].ch, 0, sizeof(trie[size].ch));trie[size].val = -1;memset(edgeSize, 0, sizeof(edgeSize));for (int i = 0; i < wordListSize; ++i) {addEdge(wordList[i]);}addEdge(beginWord);int beginId = find(beginWord), endId = find(endWord);if (endId == -1) {return 0;}int disBegin[nodeNum];memset(disBegin, -1, sizeof(disBegin));disBegin[beginId] = 0;int queBegin[nodeNum];int leftBegin = 0, rightBegin = 0;queBegin[rightBegin++] = beginId;int disEnd[nodeNum];memset(disEnd, -1, sizeof(disEnd));disEnd[endId] = 0;int queEnd[nodeNum];int leftEnd = 0, rightEnd = 0;queEnd[rightEnd++] = endId;while (leftBegin < rightBegin && leftEnd < rightEnd) {int queBeginSize = rightBegin - leftBegin;for (int i = 0; i < queBeginSize; ++i) {int nodeBegin = queBegin[leftBegin++];if (disEnd[nodeBegin] != -1) {return (disBegin[nodeBegin] + disEnd[nodeBegin]) / 2 + 1;}for (int j = 0; j < edgeSize[nodeBegin]; ++j) {if (disBegin[edge[nodeBegin][j]] == -1) {disBegin[edge[nodeBegin][j]] = disBegin[nodeBegin] + 1;queBegin[rightBegin++] = edge[nodeBegin][j];}}}int queEndSize = rightEnd - leftEnd;for (int i = 0; i < queEndSize; ++i) {int nodeEnd = queEnd[leftEnd++];if (disBegin[nodeEnd] != -1) {return (disBegin[nodeEnd] + disEnd[nodeEnd]) / 2 + 1;}for (int j = 0; j < edgeSize[nodeEnd]; ++j) {if (disEnd[edge[nodeEnd][j]] == -1) {disEnd[edge[nodeEnd][j]] = disEnd[nodeEnd] + 1;queEnd[rightEnd++] = edge[nodeEnd][j];}}}}return 0;
}