const auto new_states = state_extend_function(word,dict,visited,end);
unordered_set<string>::iterator itv;
for ( itv=new_states.begin();itv != new_states.end();itv++  ){
	string state=*itv;// state 
}

an error:

Solution. H :72:15: error: no match for ‘operator=’ (operand types are ‘STD)
Does not match on both ends of the
the equals sign, may be auto version of c + + 11 different reasons. Change the following to pass:

unordered_set<string> new_states = state_extend_function(word,dict,visited,end); 

. The complete code of the original and revised version is as follows:…

Given two words (start and end) and a dictionary, find all the shortest transformation sequences from start to end
For example:

1. can only change one letter at a time.

intermediate words in the transformation must appear in the dictionary.

Matters needing attention

1. All words have the same length.
2. All words contain only lowercase letters.

The sample
The data are as follows:
Start = “hit”
End = “cog”
Dict = [” hot “, “dot”, “dog” and “lot”, “log”]
return
[
[” hit “, “hot”, “dot”, “dog”, “cog”].
[” hit “, “hot” and “lot”, “log”, “cog”]
]

Idea: BFS.

#include <iostream>
#include <vector>
#include <limits.h>
#include <string>
#include <queue>
#include <unordered_set>
#include <unordered_map>
using namespace std;

void gen_path(unordered_map<string, vector<string> > &father,
	vector<string> &path, const string &start, const string &word,
	vector<vector<string> > &result) {
		path.push_back(word);
		if (word == start) {
			result.push_back(path);
			reverse(result.back().begin(), result.back().end());
		} else {             
			vector<string> ::iterator itfv;// for (const auto& f : father[word]) {
			for (itfv = (father[word]).begin();itfv !=(father[word]).end();itfv++ ) {
				auto f=*itfv;
				gen_path(father, path, start, f, result);
			}
		}
		path.pop_back();
}

unordered_set<string> state_extend_function(const string &s,
	const unordered_set<string> &dict, unordered_set<string> visited,string end) {
	unordered_set<string> result;
	for (size_t i = 0; i < s.size(); ++i) {
		string new_word(s);
		for (char c = 'a'; c <= 'z'; c++) {
			if (c == new_word[i]) continue;
			swap(c, new_word[i]);
			if ((dict.count(new_word) > 0 || string(new_word) == string(end) ) &&
				!visited.count(new_word)) {
					result.insert(new_word);
			}
			swap(c, new_word[i]); // 
		}
	}
	return result;
}

vector<vector<string> > findLadders(string start, string end,
	const unordered_set<string> &dict) {
		unordered_set<string> current, next; // 
		unordered_set<string> visited; // 
		unordered_map<string, vector<string> > father; // Tree
		bool found = false;
		auto state_is_target = [&](const string &s) {
			return s == end;
		};

		current.insert(start);
		while (!current.empty() && !found) {
		// Make all of this layer accessible to prevent the same layer from pointing to each other for(const auto& word:current)
			unordered_set<string>::iterator it;
			for ( it=current.begin();it != current.end();it++  ){
				string word=*it;
				visited.insert(word);
			}

			unordered_set<string>::iterator itc;
			for ( itc=current.begin();itc != current.end();itc++  ){
				string word=*itc;
				unordered_set<string> new_states = state_extend_function(word,dict,visited,end);
				unordered_set<string>::iterator itv;
				for ( itv=new_states.begin();itv != new_states.end();itv++  ){
					string state=*itv;
				
					if (state_is_target(state)) found = true;
					next.insert(state);
					father[state].push_back(word);
					// visited.insert(state); 
				}
			}
			current.clear();
			swap(current, next);
		}
		vector<vector<string> > result;
		if (found) {
			vector<string> path;
			gen_path(father, path, start, end, result);
		}
		return result;
}




void main(){
	string start="hit",end="cog";
	string sArr[]={"hot","dot","dog","lot","log"};
	int len=sizeof(sArr)/sizeof(sArr[0] );
	unordered_set<string> dict( sArr ,sArr+len);
	findLadders(start, end,dict);
	cout<<"out="<<endl;
	system("pause");
}

.
Many high-level languages have introduced the concept of lambda expressions, or anonymous functions.
.