## Question

Given two words (beginWord and endWord), and a dictionary’s word list, find the length of shortest transformation sequence from beginWord to endWord, such that:

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

For example,

Given:

beginWord = "hit" endWord = "cog" wordList = ["hot","dot","dog","lot","log"] As one shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog", return its length 5.

Note:

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

## Solution

Result: Accepted Time: 217 ms

Here should be some explanations.

class Solution {
public:
int ladderLength(string bwrd, string ewrd, unordered_set<string>& list) {
queue<int> dep;
queue<string> que;
que.push(bwrd);dep.push(1);
list.erase(bwrd);
while(!que.empty())
{
const string tmp = que.front();que.pop();
const int depth = dep.front();dep.pop();
if(tmp == ewrd)
return depth;
for(int i = 0; i < tmp.length(); i++)
{
string str = tmp;
for(char t = 'a'; t <= 'z'; t++)
{
str[i] = t;
if(list.count(str))
{
que.push(str);
list.erase(str);
dep.push(depth+1);
}
}
}
}
return 0;
}
};


Complexity Analytics

• Time Complexity: $O(?)$
• Space Complexity: $O(?)$