Word Ladder I I Algorithm
Jacob's Ladder (Hebrew: סולם יעקב Sulam Yaakov) is a ladder leading to heaven that was featured in a dream the biblical Patriarch Jacob had during his flight from his brother Esau in the book of Genesis. The meaning of the dream has been debated, but most interpretations agree that it identify Jacob with the responsibility and inheritance of the people choose by deity, as understand in Abrahamic religions.
class Solution {
private:
vector<string> vdict;
vector<vector<int>> map;
vector<vector<int>> prev;
void buildMap(const unordered_set<string>& dict) {
vdict.clear();
unordered_map<string, int> unmap;
for (auto iter = dict.begin(); iter != dict.end(); iter++) {
unmap[*iter] = vdict.size();
vdict.push_back(*iter);
}
map.clear();
map.resize(vdict.size());
for (size_t i = 0; i < vdict.size(); i++) {
string word = vdict[i];
for (size_t j = 0; j < word.size(); j++) {
for (char c = 'a'; c <= 'z'; c++) {
if (c == vdict[i][j]) continue;
word[j] = c;
if (unmap.count(word)) {
map[i].push_back(unmap[word]);
}
word[j] = vdict[i][j];
}
}
}
}
void buildReverseMap(int src, int dst) {
prev.clear();
prev.resize(vdict.size());
vector<int> dist(vdict.size());
queue<int> Q;
Q.push(src);
dist[src] = 0;
while (!Q.empty()) {
src = Q.front(); Q.pop();
if (src == dst) break;
for (size_t i = 0; i < map[src].size(); i++) {
int v = map[src][i];
if (prev[v].size() == 0) {
prev[v].push_back(src);
dist[v] = dist[src] + 1;
Q.push(v);
} else if (dist[v] == dist[src] + 1) {
prev[v].push_back(src);
}
}
}
}
void dfs(int u, int v, vector<int>& path, vector<vector<string>>& result) {
path.push_back(v);
if (u == v && path.size()) {
vector<string> pathstring;
for (auto iter = path.rbegin(); iter != path.rend(); iter++) {
pathstring.push_back(vdict[*iter]);
}
result.push_back(pathstring);
} else {
for (size_t i = 0; i < prev[v].size(); i++)
dfs(u, prev[v][i], path, result);
}
path.pop_back();
}
public:
vector<vector<string>> findLadders(string start, string end, unordered_set<string> &dict) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
dict.insert(start);
dict.insert(end);
buildMap(dict);
int src, dst;
for (src = 0; start != vdict[src]; src++);
for (dst = 0; end != vdict[dst]; dst++);
buildReverseMap(src, dst);
vector<vector<string>> result;
vector<int> path;
dfs(src, dst, path, result);
return move(result);
}
};
