New Problem "Two Sum III - Data structure design"

Author: haoel

src/twoSum/twoSum.III.cpp

@@ -0,0 +1,43 @@
+// Source : https://oj.leetcode.com/problems/two-sum-iii-data-structure-design/
+// Author : Hao Chen
+// Date   : 2014-12-29
+
+/********************************************************************************** 
+* 
+* Design and implement a TwoSum class. It should support the following operations: add and find.
+* 
+* add - Add the number to an internal data structure.
+* find - Find if there exists any pair of numbers which sum is equal to the value.
+* 
+* For example,
+*
+*   add(1); add(3); add(5);
+*   find(4) -> true
+*   find(7) -> false
+* 
+**********************************************************************************/
+
+class TwoSum {
+    private:
+        unordered_map<int, int> nums;
+    public:
+
+        //O(1) add
+        void add(int number) {
+            nums[number]++;
+        }
+
+        //O(n) find
+        bool find(int value) {
+            int one, two;
+            for(auto it = nums.begin(); it != nums.end(); it++){
+                one = it->first;
+                two = value - one;
+                if ( (one == two && it->second > 1) ||
+                        (one != two && nums.find(two) != nums.end() ) ){
+                    return true;
+                }
+            }
+            return false;
+        }
+};