Added Custom Sort String problem

Author: Karnika06

Hashing/IsomorphicStrings.java

@@ -0,0 +1,82 @@
+/* Implementation of Custom Sort String program code using java
+ * 
+ * You are given two strings order and str. All the words of order are unique and 
+ * were sorted in some custom order previously.
+
+ * Permute the characters of str so that they match the order that order was sorted. 
+ * More specifically, if a character x occurs before a character y in order, then x 
+ * should occur before y in the permuted string.
+
+ * Return any permutation of str that satisfies this property.
+ * 
+ * Problem link: https://leetcode.com/problems/custom-sort-string/
+ * 
+ */
+
+import java.util.*;
+import java.io.*;
+
+class CustomSortString 
+{
+    // this function will return any permutation of str so that they match the order that
+    // order is sorted
+    public String customSortString(String order, String str) 
+    {
+       int []freq =new int[26];
+        
+        // determining the frequency of each character
+        for(char c: str.toCharArray())
+            freq[c-'a']++;
+        
+        StringBuilder ans = new StringBuilder();
+        
+        // appending the characters in order to ans
+        for(char orderChar: order.toCharArray()) 
+        {
+            while(freq[orderChar-'a']>0)
+            {
+                ans.append(orderChar);
+                freq[orderChar-'a']--;
+            }
+        }
+        
+        //Adding the rest of the characters
+        for(int i=0;i<26;i++)
+        {
+            int freqC = freq[i];
+            while(freqC>0)
+            {
+                ans.append((char)(i+'a'));
+                freqC--;
+            }
+        }
+        // returning the resultant string
+        return ans.toString();
+    }
+    
+    public static void main()
+    {
+        Scanner sc=new Scanner(System.in);
+        String s = sc.next();
+        String t = sc.next();
+        CustomSortString obj = new CustomSortString();
+        System.out.println(obj.customSortString(s,t));
+    }
+}
+
+/*
+ * Example 1:
+ * 
+ * Input: order = "cba", s = "abcd"
+ * Output: "cbad"
+ * Explanation: 
+ * "a", "b", "c" appear in order, so the order of "a", "b", "c" should be "c", "b", and "a". 
+ * Since "d" does not appear in order, it can be at any position in the returned string. "dcba", "cdba", "cbda" are also valid outputs.
+ * 
+ * Example 2:
+ * 
+ * Input: order = "cbafg", s = "abcd"
+ * Output: "cbad"
+ * 
+ * Time Complexity: O(order.length + str.length)
+ */