[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/