word ladder

Author: chen0040

.idea/workspace.xml

@@ -389,3 +389,4 @@ codes may not be optimized
 1. [Longest Absolute File Path](https://leetcode.com/problems/longest-absolute-file-path/description/)
 1. [Maximum Product of Word Length](https://leetcode.com/problems/maximum-product-of-word-lengths/description/)
 1. [Single Number II](https://leetcode.com/problems/single-number-ii/description/)
+1. [Word Ladder](https://leetcode.com/problems/word-ladder/description/)

README.md

@@ -0,0 +1,92 @@
+package com.github.chen0040.leetcode.day18.medium;
+
+
+import java.util.*;
+
+
+/**
+ * Created by xschen on 13/8/2017.
+ *
+ * link: https://leetcode.com/problems/word-ladder/description/
+ */
+public class WordLadder {
+
+   static class Graph {
+      Map<String, List<String>> adjList = new HashMap<String, List<String>>();
+      public void addEdge(String v, String w) {
+         adj(v).add(w);
+         adj(w).add(v);
+      }
+
+      public List<String> adj(String v){
+         if(adjList.containsKey(v)){
+            return adjList.get(v);
+         } else {
+            List<String> list = new ArrayList<String>();
+            adjList.put(v, list);
+            return list;
+         }
+      }
+
+      public int search(String s, String t) {
+         Set<String> marked = new HashSet<String>();
+         Map<String, Integer> costs = new HashMap<String, Integer>();
+         Queue<String> queue = new LinkedList<String>();
+         queue.add(s);
+         costs.put(s, 0);
+         while(!queue.isEmpty()) {
+            String v= queue.remove();
+            //System.out.println(v);
+            List<String> adj_v = adj(v);
+            marked.add(v);
+            if(v.equals(t)) break;
+            for(String w : adj_v){
+               if(costs.getOrDefault(w, Integer.MAX_VALUE / 2) > costs.get(v) + 1) {
+                  costs.put(w, costs.get(v) + 1);
+                  if(!marked.contains(w)) {
+                     queue.add(w);
+                  }
+               }
+            }
+         }
+
+         if(costs.containsKey(t)) {
+            return costs.get(t) + 1;
+         } else {
+            return 0;
+         }
+      }
+   }
+
+   public class Solution {
+
+
+
+      public int ladderLength(String beginWord, String endWord, List<String> wordList) {
+         Graph g = new Graph();
+         wordList.add(beginWord);
+         for(int i=0; i < wordList.size(); ++i) {
+            String w1 = wordList.get(i);
+            for(int j=i+1; j < wordList.size(); ++j) {
+               String w2 = wordList.get(j);
+               if(isConnected(w1, w2)) {
+                  g.addEdge(w1, w2);
+               }
+            }
+         }
+
+         return g.search(beginWord, endWord);
+      }
+
+      private boolean isConnected(String w1, String w2) {
+         if(w1.length() != w2.length()) return false;
+         int count = 0;
+         for(int i=0; i < w1.length(); ++i) {
+            if(w1.charAt(i) != w2.charAt(i)) {
+               count++;
+            }
+         }
+         return count==1;
+      }
+   }
+}