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+1\. Two Sum
+
+Easy
+
+Given an array of integers `nums` and an integer `target`, return _indices of the two numbers such that they add up to `target`_.
+
+You may assume that each input would have **_exactly_ one solution**, and you may not use the _same_ element twice.
+
+You can return the answer in any order.
+
+**Example 1:**
+
+**Input:** nums = \[2,7,11,15\], target = 9
+
+**Output:** \[0,1\]
+
+**Output:** Because nums\[0\] + nums\[1\] == 9, we return \[0, 1\]. 
+
+**Example 2:**
+
+**Input:** nums = \[3,2,4\], target = 6
+
+**Output:** \[1,2\] 
+
+**Example 3:**
+
+**Input:** nums = \[3,3\], target = 6
+
+**Output:** \[0,1\] 
+
+**Constraints:**
+
+* `2 <= nums.length <= 104`
+* `-109 <= nums[i] <= 109`
+* `-109 <= target <= 109`
+* **Only one valid answer exists.**
+
+**Follow-up:** Can you come up with an algorithm that is less than `O(n2) `time complexity?
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diff --git a/src/main/java/g0001_0100/s0002_add_two_numbers/readme.md b/src/main/java/g0001_0100/s0002_add_two_numbers/readme.md
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+2\. Add Two Numbers
+
+Medium
+
+You are given two **non-empty** linked lists representing two non-negative integers. The digits are stored in **reverse order**, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.
+
+You may assume the two numbers do not contain any leading zero, except the number 0 itself.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2020/10/02/addtwonumber1.jpg)
+
+**Input:** l1 = \[2,4,3\], l2 = \[5,6,4\]
+
+**Output:** \[7,0,8\] **Explanation:** 342 + 465 = 807. 
+
+**Example 2:**
+
+**Input:** l1 = \[0\], l2 = \[0\]
+
+**Output:** \[0\] 
+
+**Example 3:**
+
+**Input:** l1 = \[9,9,9,9,9,9,9\], l2 = \[9,9,9,9\]
+
+**Output:** \[8,9,9,9,0,0,0,1\] 
+
+**Constraints:**
+
+* The number of nodes in each linked list is in the range `[1, 100]`.
+* `0 <= Node.val <= 9`
+* It is guaranteed that the list represents a number that does not have leading zeros.
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