Word Ladder

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

1. Only one letter can be changed at a time
2. Each intermediate word must exist in the dictionary

Note

• Return 0 if there is no such transformation sequence.
• All words have the same length.
• All words contain only lowercase alphabetic characters.

Example

Given:
start = "hit"
end = "cog"
dict = ["hot","dot","dog","lot","log"]

As one shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog",
return its length 5.

 
int ladderLength(string start, string end, unordered_set<string> &dict) {
        int rounds = 1;
        queue<string> que;
        que.push(start);
        
        while(que.size() > 0)
        {
            int qSize = que.size();
            while(--qSize >=0) {
              string w = que.front();
              que.pop();
            
              if (w == end) return rounds;
            
              for (int i = 0; i < w.length(); i++) {
                char c = w[i];
                for(int j= 'a'; j <= 'z'; j++) {
                    w[i] = j;
                    if (j != c && dict.count(w) == 1) {
                       que.push(w);
                       dict.erase(w);
                    }
                }
                w[i] = c;
              }
            }
            rounds++;
        }
        
        return 0;
    }