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<span style="font-family: 'microsoft yahei', simhei, arial, sans-serif; font-size: 16px;">给定2个单词（start</span><span style="font-family: 'microsoft yahei', simhei, arial, sans-serif; font-size: 16px;">和end），和一个字典，找到最短的变换序列的长度，从start到end，这样的一次</span><span style="font-size: 16px; font-family: 'microsoft yahei', simhei, arial, sans-serif;">只有一个字母可以改变并且</span><span style="font-size: 16px; font-family: 'microsoft yahei', simhei, arial, sans-serif;">每个中间字必须存在于字典。例如，给定：</span><pre style="margin: 0px 0em 25px; padding: 8px; border: 1px solid rgb(209, 209, 232); font-size: 13px; border-radius: 4px; color: rgb(34, 34, 34); line-height: 25.5px; background-color: rgb(250, 248, 227);">start = "hit"
end = "cog"
dict = ["hot","dot","dog","lot","log"]<span style="font-family: 'microsoft yahei', simhei, arial, sans-serif; font-size: 16px;"> </span><span style="font-family: 'microsoft yahei', simhei, arial, sans-serif; font-size: 16px;"> 程序将会找到"hit" -> "hot" -> "dot" -> "dog" -> "cog"，输出最短变换距离4</span>
package utils;import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Queue;import com.google.gson.Gson;public class WordLadder {// solution functionpublic static int ladderLength(String start, String end,HashSet<String> dict) {// saving the graph nodes on hash map.HashMap<String, GraphNode> nodes = new HashMap<>();// adding the start and the end words to the dictdict.add(start);dict.add(end);for (String word : dict) {nodes.put(word, new GraphNode(word));}// update each node's adjacents according to one character different// relationObject[] dictArray = dict.toArray();for (int i = 0; i < dictArray.length; i++) {for (int j = i + 1; j < dictArray.length; j++) {if (isNeighbor((String) dictArray[i], (String) dictArray[j])) {nodes.get((String) dictArray[i]).childs.add(nodes.get((String) dictArray[j]));nodes.get((String) dictArray[j]).childs.add(nodes.get((String) dictArray[i]));}}}// Run BFS on the Graph and take the dist generated as resultHashMap<String, Integer> result = BFS(nodes, start);// Return the distance of the end word node from the start word nodereturn result.get(end);}// BFS functionpublic static HashMap<String, Integer> BFS(HashMap<String, GraphNode> nodes, String start) {HashMap<String, Integer> visited = new HashMap<>();HashMap<String, Integer> dist = new HashMap<>();for (String key : nodes.keySet()) {visited.put(key, 0);dist.put(key, 0);}Queue<String> q = new LinkedList<>();q.add(start);visited.put(start, 1);while (!q.isEmpty()) {String dequeued = q.remove();GraphNode curNode = nodes.get(dequeued);LinkedList<GraphNode> currAdjs = curNode.childs;for (int i = 0; i < currAdjs.size(); i++) {GraphNode adj = (GraphNode) currAdjs.get(i);if (visited.get(adj.word) == 0) {visited.put(adj.word, 1);dist.put(adj.word, dist.get(dequeued) + 1);q.add(adj.word);}}}return dist;}// check if two words differ by one characterpublic static boolean isNeighbor(String a, String b) {assert a.length() == b.length();int differ = 0;for (int i = 0; i < a.length(); i++) {if (a.charAt(i) != b.charAt(i))differ++;if (differ > 1)return false;}return true;}public static void main(String[] args) {// dict = ["hot","dot","dog","lot","log"] result 5;HashSet<String> dict = new HashSet<String>();dict.add("hot");dict.add("dot");dict.add("dog");dict.add("lot");dict.add("log");System.out.println(ladderLength("hit", "cog", dict));}}class GraphNode {String word;LinkedList<GraphNode> childs;public GraphNode(String word) {this.word = word;childs = new LinkedList<GraphNode>();}}
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