Given two words (beginWord and endWord), and a dictionary, find the length of
shortest transformation sequence from beginWord to endWord, 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"]
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.
从前向后将字符串的字母替换,直至最后得到想要的字符串。
public int ladderLength(String start, String end, Set<String> dict) {
if (dict == null || dict.size() == 0)
return 0;
Queue<String> queue = new LinkedList<String>();
queue.offer(start);
dict.remove(start);
int length = 1;
while(!queue.isEmpty()) {
int count = queue.size();
for (int i = 0; i<count; i++){
String current = queue.poll();
for (char c = 'a'; c <= 'z'; c++) {
for (int j=0; j < current.length(); j++) {
if (c == current.charAt(j))
continue;
String tmp = replace(current, j, c);
if (tmp.equals(end))
return length + 1;
if (dict.contains(tmp)){
queue.offer(tmp);
dict.remove(tmp);
}
}
}
}
length++;
}
return 0;
}
private String replace(String s, int index, char c) {
char[] chars = s.toCharArray();
chars[index] = c;
return new String(chars);
}