Find-The-Difference Problem Pull Req (#129)

* added c++ solution for Find-The-Difference problem

* Added Find The Difference problem to README

Added Find The Difference problem to the Hashtable section

Author: HoangJames

C++/Find-The-Difference.cpp

@@ -0,0 +1,42 @@
+//time complexity O(n+m) where n and m are the number of input characters in each input string respectively
+//space compexity is O(1) since there is a limit on number of possible unique characters
+//loop through the first string and add a count of characters to hashmap
+//loop through second string and for each letter lookup in hashmap. If found, decrement the count in the hasmap. If the count <0 for any letter then we have found our extra character
+//else if the letter cannot be found in our hashmap, then this must be the extra character
+//Otherwise if no differences can be found between the two input strings we just return null character
+
+
+
+class Solution {
+public:
+    char findTheDifference(string s, string t) {
+        
+    char returnChar= '\0';
+    std::unordered_map <char,int>ourMap;
+
+    //count the letters in the input string and add it to map
+    for (const char& letter:s) {
+
+        if(ourMap.find(letter)==ourMap.end()){ ourMap[letter]=1;}
+        else{ourMap[letter]++;}
+    }
+
+        
+    //compare with letters in other string
+    for (const char& letter:t){
+        
+        //if you can find the letter then decrement it 
+        if(ourMap.find(letter)!=ourMap.end()) { 
+        
+            ourMap[letter]--; 
+            if(ourMap[letter]<0) { return letter; } 
+        
+        }
+        
+        else{return letter;}
+    }
+        
+    return returnChar;
+        
+    }
+};

README.md

@@ -240,6 +240,7 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 049 | [Group Anagrams](https://leetcode.com/problems/group-anagrams/)         | [Python](./Python/group_anagram.py)                                                           | _O(nlogn)_  | _O(1)_ | Easy       |     |
 | 554 | [Brick Wall](https://leetcode.com/problems/brick-wall/)                 | [C++](./C++/brick-walls.cpp)                                                                  | _O(n)_      | _O(n)_ | Medium     |     |
 | 146 | [LRU Cache](https://leetcode.com/problems/lru-cache/)                   | [Javascript](../JavaScript/146.LRU-Cache.js)                                                  | _O(log(n))_ | _O(n)_ | Medium     |     |
+| 389 | [Find The Difference](https://leetcode.com/problems/find-the-difference/)                   | [C++](../C++/Find-The-Difference.cpp)                                                  | _O(n)_ | _O(1)_ | Easy     |     |
 
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