[LeetCode] Word Ladder II 之一

class Solution {
public:
vector< vector<string> > findLadders( string start, string end, unordered_set<string > &dict) {

vector< vector< string>  >  ret;
vector<string> path;
if( start == end ) {
path.push_back(start);
ret.push_back(path);
return ret;
}
else  if(dict.empty()){
return ret;
}
unordered_set<string> vis;
path.push_back(start);
vis.insert(start);
dfs(start,end,dict,path, vis, ret);

return ret;
}

private:
// 修改了函数参数
void  dfs( string start, string end, const unordered_set<string>& dict,
vector<string>&  path, unordered_set<string>&  vis,vector<vector<string>  >&  ret )
{
size_t len = start.size();
for( int i = 0;i < len ;i++)
{
for( char j = 'a' ; j <= 'z' ;j++)
{

if( j == start[i]){
continue;
}
string  tmp = start;
tmp[i] = j ;

if( tmp == end) {
path.push_back(end);
if(  ret.empty()  || ret[0].size() == path.size() ){
ret.push_back(path);
}
else if( ret[0].size() > path.size() )    {
ret.clear();
ret.push_back(path);
}
path.pop_back();

return;

}

if (  dict.count(tmp) == 0 || vis.count(tmp) != 0 ) {
continue;
}

path.push_back(tmp);
vis.insert(tmp);

dfs(tmp,end,dict,path,vis,ret);

path.pop_back();
vis.erase(tmp);

}

}
}
};