Added leetcode solution for Buddy Strings (#128)

Author: SauravP97

Java/buddy-strings.java

@@ -0,0 +1,50 @@
+/** 
+ *  Problem Name : Buddy Strings
+ *  Concept Involved : String Manipulation, Frequency Computation, Observation
+ * 
+ *  Execution Time : 2 ms
+ *  Memory Consumed : 39.1 mb
+ * 
+*/
+class Solution {
+    public boolean isDuplicate(String str){
+        int[] fre = new int[26];
+        for(int i=0; i<str.length(); i++){
+            int ind = str.charAt(i) - 'a';
+            fre[ind]++;
+            if(fre[ind] > 1){
+                return true;
+            }
+        }
+        return false;
+    }
+    public boolean buddyStrings(String A, String B) {
+        if(A.length() != B.length()){
+            return false;
+        }
+        
+        int count = 0;
+        char ca = 'A';
+        char cb = 'A';
+        
+        for(int i=0; i<A.length(); i++){
+            if(A.charAt(i) != B.charAt(i) ){
+                if(count == 0){
+                    ca = A.charAt(i);
+                    cb = B.charAt(i);
+                }
+                else if(count == 1){
+                    if(ca != B.charAt(i) || cb != A.charAt(i)){
+                        count++;
+                    }
+                }
+                count++;
+            }
+        }
+        
+        if(count == 2 || (count == 0 && isDuplicate(A))){
+            return true;
+        }
+        return false;
+    }
+}

README.md

@@ -143,7 +143,7 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 1221 | [Split a String in Balanced Strings](https://leetcode.com/problems/split-a-string-in-balanced-strings/)                                         | [Python](./Python/split-a-string-in-balanced-strings.py)                   | _O(n)_ | _O(1)_ | Easy       |     |                 |
 | 1614 | [Maximum Nesting Depth of the Parentheses](https://leetcode.com/problems/maximum-nesting-depth-of-the-parentheses/)                             | [Java](./Java/max-nesting-depth-parentheses.java)                          | _O(n)_ | _O(1)_ | Easy       |     |                 |
 | 1374 | [Generate a String With Characters That Have Odd Counts](https://leetcode.com/problems/generate-a-string-with-characters-that-have-odd-counts/) | [Java](./Java/generate-a-string-with-characters-that-have-odd-counts.java) | _O(n)_ | _O(1)_ | Easy       |     |                 |
-
+| 859 | [Buddy Strings](https://leetcode.com/problems/buddy-strings/) | [Java](./Java/buddy-strings.java) | _O(n)_ | _O(1)_ | Easy       |     |                 |
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