Question

[Write a Java Program]

This question is kind of like this Word Ladder question (similar, but not exactly same) at here: https://leetcode.com/problems/word-ladder/description/

and its solution (could be a hint) is at here: https://leetcode.com/problems/word-ladder/discuss/

Write a java program for the following task. Many thanks! Question is:

Answer 1

class WordNode{
    String word;
    int numSteps;
    WordNode pre;
 
    public WordNode(String word, int numSteps, WordNode pre){
        this.word = word;
        this.numSteps = numSteps;
        this.pre = pre;
    }
}
 
public class Solution {
    public List<List<String>> findLadders(String start, String end, Set<String> dict) {
        List<List<String>> result = new ArrayList<List<String>>();
 
        LinkedList<WordNode> queue = new LinkedList<WordNode>();
        queue.add(new WordNode(start, 1, null));
 
        dict.add(end);
 
        int minStep = 0;
 
        HashSet<String> visited = new HashSet<String>();  
        HashSet<String> unvisited = new HashSet<String>();  
        unvisited.addAll(dict);
 
        int preNumSteps = 0;
 
        while(!queue.isEmpty()){
            WordNode top = queue.remove();
            String word = top.word;
            int currNumSteps = top.numSteps;
 
            if(word.equals(end)){
                if(minStep == 0){
                    minStep = top.numSteps;
                }
 
                if(top.numSteps == minStep && minStep !=0){
                    //nothing
                    ArrayList<String> t = new ArrayList<String>();
                    t.add(top.word);
                    while(top.pre !=null){
                        t.add(0, top.pre.word);
                        top = top.pre;
                    }
                    result.add(t);
                    continue;
                }
 
            }
 
            if(preNumSteps < currNumSteps){
                unvisited.removeAll(visited);
            }
 
            preNumSteps = currNumSteps;
 
            char[] arr = word.toCharArray();
            for(int i=0; i<arr.length; i++){
                for(char c='a'; c<='z'; c++){
                    char temp = arr[i];
                    if(arr[i]!=c){
                        arr[i]=c;
                    }
 
                    String newWord = new String(arr);
                    if(unvisited.contains(newWord)){
                        queue.add(new WordNode(newWord, top.numSteps+1, top));
                        visited.add(newWord);
                    }
 
                    arr[i]=temp;
                }
            }
 
 
        }
 
        return result;
    }
}