1 class Solution {
2 public:
3 typedef unordered_map<string, unsigned> MyHashMap;
4 typedef unordered_map<string, vector<string>> SVMap;
5 vector<vector<string>> findLadders(string start, string end, unordered_set<string> &dict) {
6 // Note: The Solution object is instantiated only once and is reused by each test case.
7 unsigned rltLen = INT_MAX;
8 vector<vector<string> > rlt;
9 if (start == end)
10 rltLen = 2;
11 if (start.length() != end.length())
12 return rlt;
13 queue<string> qs;
14 int len = start.length();
15 qs.push(start);
16 MyHashMap depMap;
17 SVMap prevMap;
18 prevMap[start] = vector<string>();
19 depMap[start] = 1;
20 while (!qs.empty()){
21 string cur = qs.front();
22 qs.pop();
23 unsigned curLen = depMap[cur];
24 if (curLen >= rltLen)
25 continue;
26 for (int i = 0; i < len; i++){
27 for (int j = 0; j < 26; j++){
28 string tmp = cur;
29 tmp[i] = 'a' + j;
30 if (tmp == cur)
31 continue;
32 if (tmp == end){
33 rltLen = depMap[cur]+1;
34 prevMap[end].push_back(cur);
35 continue;
36 }
37 if (dict.find(tmp) == dict.end())
38 continue;
39 if (curLen+1 >= rltLen)
40 continue;
41 MyHashMap::iterator mhi = depMap.find(tmp);
42 if (mhi!=depMap.end() && mhi->second <= curLen)
43 continue;
44 if (prevMap.find(tmp) == prevMap.end())
45 prevMap[tmp] = vector<string>(1, cur);
46 else prevMap[tmp].push_back(cur);
47 if (mhi != depMap.end())
48 continue;
49 qs.push(tmp);
50 depMap[tmp] = curLen+1;
51 }
52 }
53 } // end while
54 if (rltLen == INT_MAX)
55 return rlt;
56 stack<vector<string> > svs;
57 svs.push(vector<string>(1, end));
58 while (!svs.empty()){
59 vector<string> vs = svs.top();
60 svs.pop();
61 string last = *(vs.end() - 1);
62 if (last == start){
63 rlt.push_back(vs);
64 continue;
65 }
66 for (auto iter = prevMap[last].begin(); iter != prevMap[last].end(); iter++){
67 vector<string> tmpVect = vs;
68 tmpVect.push_back(*iter);
69 svs.push(tmpVect);
70 }
71 }
72 for (auto iter = rlt.begin(); iter != rlt.end(); iter++){
73 int size = iter->size();
74 int j = size / 2;
75 for (int i = 0; i < j; i++){
76 string tmp = (*iter)[i];
77 (*iter)[i] = (*iter)[size - i - 1];
78 (*iter)[size - i - 1] = tmp;
79 }
80 }
81 return rlt;
82 }
83 };
