[Leetcode] World Ladder

Given two words (start and end), and a dictionary, find all shortest transformation sequence(s) from start to end, such that:
  
  
  
  

   
   
   
   
Only one letter can be changed at a time
   
   
   
   
Each intermediate word must exist in the dictionary
  
  
  
  
For example,
Given:
start = "hit"
end = "cog"
dict = ["hot","dot","dog","lot","log"]
Return
  [
    ["hit","hot","dot","dog","cog"],
    ["hit","hot","lot","log","cog"]
  ]
Note:

  
  
  
  

   
   
   
   
All words have the same length.
   
   
   
   
All words contain only lowercase alphabetic characters.
  
  
  
  

ANSWER:

class Solution {
public:
    vector<vector<string>> findLadders(string start, string end, unordered_set<string> &dict) {
        vector<string> currentseq;
        int shortest=dict.size()+1;
        vector<vector<string>> resultseqs;
        int currentsteps=0;
        
        helper(start,end,dict,shortest,currentsteps,currentseq,resultseqs);
        return resultseqs;
    }
    
    void helper(string start, string end, unordered_set<string> &dict, int &shortest, int currentsteps, vector<string> currentseq, vector<vector<string>> &resultseqs)
    {
        currentseq.push_back(start);
        
        if(start==end && currentsteps < shortest)
        {
            resultseqs.clear();
            shortest=currentsteps;
            resultseqs.push_back(currentseq);
        }
        else if(start==end && currentsteps == shortest)
        {
            resultseqs.push_back(currentseq);
        }
        else if(start==end || currentsteps==dict.size())
            return;
            
        //traverse throughput the dict to find one-change strings
        auto a=dict.begin(); //用迭代器遍历一个unsorted_set         string strdict;         for(int i=0;i<dict.size();i++)         {             strdict= *a;             if(noexist(currentseq,strdict) && oneChange(start,strdict))             {                  helper(strdict,end,dict,shortest,currentsteps+1,currentseq,resultseqs);             }                          a++;         }
    }
    
    bool noexist(vector<string> strsets, string str)
    {
        for(int i=0;i<strsets.size();i++)
        {
            if(strsets.at(i) == str)
               return false;
        }
        return true;
    }
    
    bool oneChange(string a, string b)
    {
        if(a.length()!=b.length()) return false;
        
        int samecnt=0;
        for(int i=0;i<a.length();i++)
        {
            if(a[i] == b[i])
              samecnt++;
        }
        
        if(samecnt==a.length()-1)
           return true;
        else
           return false;
    }
};
unsorted_set<int/string/...> 用法: http://www.cplusplus.com/reference/unordered_set/unordered_set/