Added missing READMEs

Author: orhtej2

contains-duplicate/README.md

@@ -0,0 +1,29 @@
+# 217. Contains Duplicate
+
+[LeetCode link](https://leetcode.com/problems/contains-duplicate/)
+
+Given an integer array `nums`, return `true` if any value appears **at least twice** in the array, and return `false` if every element is distinct.
+
+### Example 1:
+
+> **Input:** `nums = [1,2,3,1]`
+>
+> **Output:** `true`
+
+### Example 2:
+
+> **Input:** `nums = [1,2,3,4]`
+>
+> **Output:** `false`
+
+### Example 3:
+
+> **Input:** `nums = [1,1,1,3,3,4,3,2,4,2]`
+>
+> **Output:** `true`
+
+### Constraints:
+
+> - 1 <= `nums.length` <= 105
+> - -109 <= `nums[i]` <= 109
+

longest-substring-without-repeating-characters/README.md

@@ -0,0 +1,41 @@
+# 3. Longest Substring Without Repeating Characters
+
+[LeetCode Link](https://leetcode.com/problems/longest-substring-without-repeating-characters/)
+
+Given a string s, find the length of the longest
+substring without repeating characters.
+
+### Example 1:
+
+> **Input:** `s = "abcabcbb"`
+>
+> **Output:** `3`
+>
+> **Explanation:** The answer is`"abc"`, with the length of `3`.
+
+### Example 2:
+
+> **Input:** `s = "bbbbb"`
+>
+> **Output:** `1`
+>
+> **Explanation:** The answer is `"b"`, with the length of `1`.
+
+### Example 3:
+
+> **Input:** `s = "pwwkew"`
+>
+> **Output:** `3`
+>
+> **Explanation:** The answer is `"wke"`, with the length of `3`.
+>
+> Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.
+
+
+### Constraints:
+
+ - 0 <= `s.length` <= 5 * 104
+ - `s` consists of English letters, digits, symbols and spaces.
+
+
+

roman-numerals/README.md

@@ -0,0 +1,61 @@
+# 13. Roman to Integer
+
+[LeetCode Link](https://leetcode.com/problems/roman-to-integer/)
+
+Roman numerals are represented by seven different symbols: `I`, `V`, `X`, `L`, `C`, `D` and `M`.
+
+```
+Symbol       Value
+I             1
+V             5
+X             10
+L             50
+C             100
+D             500
+M             1000
+```
+
+For example, `2` is written as `II` in Roman numeral, just two ones added together. `12` is written as `XII`, which is simply `X + II`. The number `27` is written as `XXVII`, which is `XX + V + II`.
+
+Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not `IIII`. Instead, the number four is written as `IV`. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as `IX`. There are six instances where subtraction is used:
+
+- `I` can be placed before `V` (5) and `X` (10) to make 4 and 9. 
+- `X` can be placed before `L` (50) and `C` (100) to make 40 and 90. 
+- `C` can be placed before `D` (500) and `M` (1000) to make 400 and 900.
+
+Given a roman numeral, convert it to an integer.
+
+ 
+
+### Example 1:
+
+> **Input:** `s = "III"`
+>
+> **Output:** `3`
+>
+> **Explanation:** `III = 3`.
+
+### Example 2:
+
+> **Input:** `s = "LVIII"`
+>
+> **Output:** `58`
+
+> **Explanation:** `L = 50, V= 5, III = 3`.
+
+### Example 3:
+
+> **Input:** `s = "MCMXCIV"`
+>
+> **Output:** `1994`
+>
+> **Explanation:** `M = 1000, CM = 900, XC = 90 and IV = 4`.
+
+ 
+
+### Constraints:
+
+ - 1 <= `s.length` <= 15
+ - `s` contains only the characters (`'I'`, `'V'`, `'X'`, `'L'`, `'C'`, `'D'`, `'M'`).
+ - It is guaranteed that `s` is a valid roman numeral in the range `[1, 3999]`.
+