Added two sum solution in CPP using map

leetcode/1 - twosum/two_sum.cpp

@@ -0,0 +1,54 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+/**
+ * The Two Sum problem can be solved using a map to store each index
+ * 
+ * In the following approach, the C++ Map can store each index in O (Log N)
+ * The trick in this question is start to store index from last index to index 1,
+ * just to deal with repeated values. The other point is just get all indexes in O (N)
+ * 
+ * After that, you can loop through array getting the remainder and check if
+ * there is this velor in the array
+ * 
+ * Complexity Time: O (N log N)
+ * 
+ * Note: Its possible solve this problem using Binary Search as well,
+ * you just need to be careful with negative values. The complexity time
+ * will be O (N log N) as well.
+ * 
+ */ 
+
+vector<int> twoSum(vector<int>& nums, int target) {
+   map<int, int> mapAux;
+
+  for(int i = nums.size() - 1; i >= 1; i--) {
+    mapAux[nums[i]] = i;
+  } 
+
+  for(int i = 0; i < nums.size(); i++) {
+    int rem = target - nums[i];
+    int remPos = mapAux[rem];
+
+    if(nums[remPos] == rem && remPos != i) {
+      vector<int> answer = {i, remPos};
+
+      return answer;
+    }
+  }
+
+  return vector<int>();
+}
+
+int main () {
+
+  vector<int> nums = {2, 7, 11, 15};
+  int target = 9;
+
+  auto answer = twoSum(nums, target);
+
+  cout << answer[0] << " " << answer[1] << endl; 
+
+  return 0;
+}