BFS Solution added (#80)

* Added the file

* Added word-ladder program

* Update README.md

Author: ATRI2107

Java/word-ladder.java

@@ -0,0 +1,57 @@
+/*
+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:
+
+Only one letter can be changed at a time.
+Each transformed word must exist in the word list.
+Note:
+
+Return 0 if there is no such transformation sequence.
+All words have the same length.
+All words contain only lowercase alphabetic characters.
+You may assume no duplicates in the word list.
+You may assume beginWord and endWord are non-empty and are not the same.
+
+Problem Link:  https://leetcode.com/problems/word-ladder/
+It is a popular interview program which is based on BFS
+*/
+import java.util.*;
+class Solution {
+    public int ladderLength(String beginWord, String endWord, List<String> wordList) {
+        HashSet<String> hs=new HashSet<>(wordList);
+        if(!hs.contains(endWord))
+        {
+            return 0;
+        }
+        int steps=1;
+        Queue<String> q=new LinkedList<>();
+        q.add(beginWord);
+        while(!q.isEmpty())
+        {
+            int count=q.size();
+            for(int i=0;i<count;i++)
+            {
+                String curr=q.poll();
+                char a[]=curr.toCharArray();
+                for(int j=0;j<a.length;j++)
+                {
+                    char temp=a[j];
+                    for(char c='a';c<='z';c++)
+                    {
+                        if(a[j]==c) continue;
+                        a[j]=c;
+                        String test=new String(a);
+                        if(test.equals(endWord)) return steps+1;
+                        if(hs.contains(test))
+                        {
+                            q.add(test);
+                            hs.remove(test);
+                        }
+                    }
+                    a[j]=temp;
+                }
+            }
+            steps++;
+        }
+        return 0;
+    }
+}

README.md

@@ -254,6 +254,7 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | ---- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------- | ------------------------- | ----------------- | ---------- | --- | ---- |
 | 1284 | [Minimum Number of Flips to Convert Binary Matrix to Zero Matrix](https://leetcode.com/problems/minimum-number-of-flips-to-convert-binary-matrix-to-zero-matrix/) | [C++](./C++/Minimum-Number-of-Flips-to-Convert-Binary-Matrix-to-Zero-Matrix.cpp) | _O(m * n * 2 ^ (m \* n))_ | _O(2 ^ (m \* n))_ | Hard       | BFS |      |
 | 200  | [Number of Islands](https://leetcode.com/problems/number-of-islands/)                                                                                             | [Java](./Java/NumberOfIslands.java)                                              | O(R \* C)                 | O(R \* C)         | Medium     | BFS |
+| 200  | [Word Ladder](https://leetcode.com/problems/word-ladder/)                                                                                             | [Java](./Java/word-ladder.java)                                              | O(N^2 \* M)                 | O(N \* M)         | Medium     | BFS |
 
 <br/>
 <div align="right">