diff --git a/src/main/java/g0001_0100/s0031_next_permutation/readme.md b/src/main/java/g0001_0100/s0031_next_permutation/readme.md
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@@ -0,0 +1,38 @@
+31\. Next Permutation
+
+Medium
+
+Implement **next permutation**, which rearranges numbers into the lexicographically next greater permutation of numbers.
+
+If such an arrangement is not possible, it must rearrange it as the lowest possible order (i.e., sorted in ascending order).
+
+The replacement must be **[in place](http://en.wikipedia.org/wiki/In-place_algorithm)** and use only constant extra memory.
+
+**Example 1:**
+
+**Input:** nums = \[1,2,3\]
+
+**Output:** \[1,3,2\] 
+
+**Example 2:**
+
+**Input:** nums = \[3,2,1\]
+
+**Output:** \[1,2,3\] 
+
+**Example 3:**
+
+**Input:** nums = \[1,1,5\]
+
+**Output:** \[1,5,1\] 
+
+**Example 4:**
+
+**Input:** nums = \[1\]
+
+**Output:** \[1\] 
+
+**Constraints:**
+
+* `1 <= nums.length <= 100`
+* `0 <= nums[i] <= 100`
\ No newline at end of file
diff --git a/src/main/java/g0001_0100/s0032_longest_valid_parentheses/readme.md b/src/main/java/g0001_0100/s0032_longest_valid_parentheses/readme.md
new file mode 100644
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+++ b/src/main/java/g0001_0100/s0032_longest_valid_parentheses/readme.md
@@ -0,0 +1,32 @@
+32\. Longest Valid Parentheses
+
+Hard
+
+Given a string containing just the characters `'('` and `')'`, find the length of the longest valid (well-formed) parentheses substring.
+
+**Example 1:**
+
+**Input:** s = "(()"
+
+**Output:** 2
+
+**Explanation:** The longest valid parentheses substring is "()". 
+
+**Example 2:**
+
+**Input:** s = ")()())"
+
+**Output:** 4
+
+**Explanation:** The longest valid parentheses substring is "()()". 
+
+**Example 3:**
+
+**Input:** s = ""
+
+**Output:** 0 
+
+**Constraints:**
+
+* `0 <= s.length <= 3 * 104`
+* `s[i]` is `'('`, or `')'`.
\ No newline at end of file
diff --git a/src/main/java/g0001_0100/s0033_search_in_rotated_sorted_array/readme.md b/src/main/java/g0001_0100/s0033_search_in_rotated_sorted_array/readme.md
new file mode 100644
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+++ b/src/main/java/g0001_0100/s0033_search_in_rotated_sorted_array/readme.md
@@ -0,0 +1,37 @@
+33\. Search in Rotated Sorted Array
+
+Medium
+
+There is an integer array `nums` sorted in ascending order (with **distinct** values).
+
+Prior to being passed to your function, `nums` is **possibly rotated** at an unknown pivot index `k` (`1 <= k < nums.length`) such that the resulting array is `[nums[k], nums[k+1], ..., nums[n-1], nums[0], nums[1], ..., nums[k-1]]` (**0-indexed**). For example, `[0,1,2,4,5,6,7]` might be rotated at pivot index `3` and become `[4,5,6,7,0,1,2]`.
+
+Given the array `nums` **after** the possible rotation and an integer `target`, return _the index of_ `target` _if it is in_ `nums`_, or_ `-1` _if it is not in_ `nums`.
+
+You must write an algorithm with `O(log n)` runtime complexity.
+
+**Example 1:**
+
+**Input:** nums = \[4,5,6,7,0,1,2\], target = 0
+
+**Output:** 4 
+
+**Example 2:**
+
+**Input:** nums = \[4,5,6,7,0,1,2\], target = 3
+
+**Output:** -1 
+
+**Example 3:**
+
+**Input:** nums = \[1\], target = 0
+
+**Output:** -1 
+
+**Constraints:**
+
+* `1 <= nums.length <= 5000`
+* `-104 <= nums[i] <= 104`
+* All values of `nums` are **unique**.
+* `nums` is an ascending array that is possibly rotated.
+* `-104 <= target <= 104`
\ No newline at end of file
diff --git a/src/main/java/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/readme.md b/src/main/java/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/readme.md
new file mode 100644
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+++ b/src/main/java/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/readme.md
@@ -0,0 +1,34 @@
+34\. Find First and Last Position of Element in Sorted Array
+
+Medium
+
+Given an array of integers `nums` sorted in non-decreasing order, find the starting and ending position of a given `target` value.
+
+If `target` is not found in the array, return `[-1, -1]`.
+
+You must write an algorithm with `O(log n)` runtime complexity.
+
+**Example 1:**
+
+**Input:** nums = \[5,7,7,8,8,10\], target = 8
+
+**Output:** \[3,4\] 
+
+**Example 2:**
+
+**Input:** nums = \[5,7,7,8,8,10\], target = 6
+
+**Output:** \[-1,-1\] 
+
+**Example 3:**
+
+**Input:** nums = \[\], target = 0
+
+**Output:** \[-1,-1\] 
+
+**Constraints:**
+
+* `0 <= nums.length <= 105`
+* `-109 <= nums[i] <= 109`
+* `nums` is a non-decreasing array.
+* `-109 <= target <= 109`
\ No newline at end of file
diff --git a/src/main/java/g0001_0100/s0035_search_insert_position/readme.md b/src/main/java/g0001_0100/s0035_search_insert_position/readme.md
new file mode 100644
index 000000000..daf79666f
--- /dev/null
+++ b/src/main/java/g0001_0100/s0035_search_insert_position/readme.md
@@ -0,0 +1,44 @@
+35\. Search Insert Position
+
+Easy
+
+Given a sorted array of distinct integers and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order.
+
+You must write an algorithm with `O(log n)` runtime complexity.
+
+**Example 1:**
+
+**Input:** nums = \[1,3,5,6\], target = 5
+
+**Output:** 2 
+
+**Example 2:**
+
+**Input:** nums = \[1,3,5,6\], target = 2
+
+**Output:** 1 
+
+**Example 3:**
+
+**Input:** nums = \[1,3,5,6\], target = 7
+
+**Output:** 4 
+
+**Example 4:**
+
+**Input:** nums = \[1,3,5,6\], target = 0
+
+**Output:** 0 
+
+**Example 5:**
+
+**Input:** nums = \[1\], target = 0
+
+**Output:** 0 
+
+**Constraints:**
+
+* `1 <= nums.length <= 104`
+* `-104 <= nums[i] <= 104`
+* `nums` contains **distinct** values sorted in **ascending** order.
+* `-104 <= target <= 104`
\ No newline at end of file
diff --git a/src/main/java/g0001_0100/s0036_valid_sudoku/readme.md b/src/main/java/g0001_0100/s0036_valid_sudoku/readme.md
new file mode 100644
index 000000000..2098acf48
--- /dev/null
+++ b/src/main/java/g0001_0100/s0036_valid_sudoku/readme.md
@@ -0,0 +1,58 @@
+36\. Valid Sudoku
+
+Medium
+
+Determine if a `9 x 9` Sudoku board is valid. Only the filled cells need to be validated **according to the following rules**:
+
+1. Each row must contain the digits `1-9` without repetition.
+2. Each column must contain the digits `1-9` without repetition.
+3. Each of the nine `3 x 3` sub-boxes of the grid must contain the digits `1-9` without repetition.
+
+**Note:**
+
+* A Sudoku board (partially filled) could be valid but is not necessarily solvable.
+* Only the filled cells need to be validated according to the mentioned rules.
+
+**Example 1:**
+
+![](https://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Sudoku-by-L2G-20050714.svg/250px-Sudoku-by-L2G-20050714.svg.png)
+
+**Input:**
+
+ board =
+ [["5","3",".",".","7",".",".",".","."]
+ ,["6",".",".","1","9","5",".",".","."]
+ ,[".","9","8",".",".",".",".","6","."]
+ ,["8",".",".",".","6",".",".",".","3"]
+ ,["4",".",".","8",".","3",".",".","1"]
+ ,["7",".",".",".","2",".",".",".","6"]
+ ,[".","6",".",".",".",".","2","8","."]
+ ,[".",".",".","4","1","9",".",".","5"]
+ ,[".",".",".",".","8",".",".","7","9"]]
+
+**Output:** true 
+
+**Example 2:**
+
+**Input:**
+
+ board =
+ [["8","3",".",".","7",".",".",".","."]
+ ,["6",".",".","1","9","5",".",".","."]
+ ,[".","9","8",".",".",".",".","6","."]
+ ,["8",".",".",".","6",".",".",".","3"]
+ ,["4",".",".","8",".","3",".",".","1"]
+ ,["7",".",".",".","2",".",".",".","6"]
+ ,[".","6",".",".",".",".","2","8","."]
+ ,[".",".",".","4","1","9",".",".","5"]
+ ,[".",".",".",".","8",".",".","7","9"]]
+
+**Output:** false
+
+**Explanation:** Same as Example 1, except with the **5** in the top left corner being modified to **8**. Since there are two 8's in the top left 3x3 sub-box, it is invalid. 
+
+**Constraints:**
+
+* `board.length == 9`
+* `board[i].length == 9`
+* `board[i][j]` is a digit `1-9` or `'.'`.
\ No newline at end of file
diff --git a/src/main/java/g0001_0100/s0037_sudoku_solver/readme.md b/src/main/java/g0001_0100/s0037_sudoku_solver/readme.md
new file mode 100644
index 000000000..ca744931b
--- /dev/null
+++ b/src/main/java/g0001_0100/s0037_sudoku_solver/readme.md
@@ -0,0 +1,52 @@
+37\. Sudoku Solver
+
+Hard
+
+Write a program to solve a Sudoku puzzle by filling the empty cells.
+
+A sudoku solution must satisfy **all of the following rules**:
+
+1. Each of the digits `1-9` must occur exactly once in each row.
+2. Each of the digits `1-9` must occur exactly once in each column.
+3. Each of the digits `1-9` must occur exactly once in each of the 9 `3x3` sub-boxes of the grid.
+
+The `'.'` character indicates empty cells.
+
+**Example 1:**
+
+![](https://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Sudoku-by-L2G-20050714.svg/250px-Sudoku-by-L2G-20050714.svg.png)
+
+**Input:**
+
+ board = [["5","3",".",".","7",".",".",".","."],
+ ["6",".",".","1","9","5",".",".","."],
+ [".","9","8",".",".",".",".","6","."],
+ ["8",".",".",".","6",".",".",".","3"],
+ ["4",".",".","8",".","3",".",".","1"],
+ ["7",".",".",".","2",".",".",".","6"],
+ [".","6",".",".",".",".","2","8","."],
+ [".",".",".","4","1","9",".",".","5"],
+ [".",".",".",".","8",".",".","7","9"]]
+
+**Output:**
+
+ [["5","3","4","6","7","8","9","1","2"],
+ ["6","7","2","1","9","5","3","4","8"],
+ ["1","9","8","3","4","2","5","6","7"],
+ ["8","5","9","7","6","1","4","2","3"],
+ ["4","2","6","8","5","3","7","9","1"],
+ ["7","1","3","9","2","4","8","5","6"],
+ ["9","6","1","5","3","7","2","8","4"],
+ ["2","8","7","4","1","9","6","3","5"],
+ ["3","4","5","2","8","6","1","7","9"]]
+
+**Explanation:** The input board is shown above and the only valid solution is shown below:
+
+![](https://upload.wikimedia.org/wikipedia/commons/thumb/3/31/Sudoku-by-L2G-20050714_solution.svg/250px-Sudoku-by-L2G-20050714_solution.svg.png) 
+
+**Constraints:**
+
+* `board.length == 9`
+* `board[i].length == 9`
+* `board[i][j]` is a digit or `'.'`.
+* It is **guaranteed** that the input board has only one solution.
\ No newline at end of file
diff --git a/src/main/java/g0001_0100/s0038_count_and_say/readme.md b/src/main/java/g0001_0100/s0038_count_and_say/readme.md
new file mode 100644
index 000000000..53386af59
--- /dev/null
+++ b/src/main/java/g0001_0100/s0038_count_and_say/readme.md
@@ -0,0 +1,41 @@
+38\. Count and Say
+
+Medium
+
+The **count-and-say** sequence is a sequence of digit strings defined by the recursive formula:
+
+* `countAndSay(1) = "1"`
+* `countAndSay(n)` is the way you would "say" the digit string from `countAndSay(n-1)`, which is then converted into a different digit string.
+
+To determine how you "say" a digit string, split it into the **minimal** number of groups so that each group is a contiguous section all of the **same character.** Then for each group, say the number of characters, then say the character. To convert the saying into a digit string, replace the counts with a number and concatenate every saying.
+
+For example, the saying and conversion for digit string `"3322251"`:
+
+![](https://assets.leetcode.com/uploads/2020/10/23/countandsay.jpg)
+
+Given a positive integer `n`, return _the_ `nth` _term of the **count-and-say** sequence_.
+
+**Example 1:**
+
+**Input:** n = 1
+
+**Output:** "1"
+
+**Explanation:** This is the base case. 
+
+**Example 2:**
+
+**Input:** n = 4
+
+**Output:** "1211"
+
+**Explanation:**
+
+ countAndSay(1) = "1"
+ countAndSay(2) = say "1" = one 1 = "11"
+ countAndSay(3) = say "11" = two 1's = "21"
+ countAndSay(4) = say "21" = one 2 + one 1 = "12" + "11" = "1211" 
+
+**Constraints:**
+
+* `1 <= n <= 30`
\ No newline at end of file
diff --git a/src/main/java/g0001_0100/s0039_combination_sum/readme.md b/src/main/java/g0001_0100/s0039_combination_sum/readme.md
new file mode 100644
index 000000000..64da13032
--- /dev/null
+++ b/src/main/java/g0001_0100/s0039_combination_sum/readme.md
@@ -0,0 +1,52 @@
+39\. Combination Sum
+
+Medium
+
+Given an array of **distinct** integers `candidates` and a target integer `target`, return _a list of all **unique combinations** of_ `candidates` _where the chosen numbers sum to_ `target`_._ You may return the combinations in **any order**.
+
+The **same** number may be chosen from `candidates` an **unlimited number of times**. Two combinations are unique if the frequency of at least one of the chosen numbers is different.
+
+It is **guaranteed** that the number of unique combinations that sum up to `target` is less than `150` combinations for the given input.
+
+**Example 1:**
+
+**Input:** candidates = \[2,3,6,7\], target = 7
+
+**Output:** \[\[2,2,3\],\[7\]\]
+
+**Explanation:**
+
+ 2 and 3 are candidates, and 2 + 2 + 3 = 7. Note that 2 can be used multiple times.
+ 7 is a candidate, and 7 = 7.
+ These are the only two combinations. 
+
+**Example 2:**
+
+**Input:** candidates = \[2,3,5\], target = 8
+
+**Output:** \[\[2,2,2,2\],\[2,3,3\],\[3,5\]\] 
+
+**Example 3:**
+
+**Input:** candidates = \[2\], target = 1
+
+**Output:** \[\] 
+
+**Example 4:**
+
+**Input:** candidates = \[1\], target = 1
+
+**Output:** \[\[1\]\] 
+
+**Example 5:**
+
+**Input:** candidates = \[1\], target = 2
+
+**Output:** \[\[1,1\]\] 
+
+**Constraints:**
+
+* `1 <= candidates.length <= 30`
+* `1 <= candidates[i] <= 200`
+* All elements of `candidates` are **distinct**.
+* `1 <= target <= 500`
\ No newline at end of file
diff --git a/src/main/java/g0001_0100/s0040_combination_sum_ii/readme.md b/src/main/java/g0001_0100/s0040_combination_sum_ii/readme.md
new file mode 100644
index 000000000..974e1d907
--- /dev/null
+++ b/src/main/java/g0001_0100/s0040_combination_sum_ii/readme.md
@@ -0,0 +1,39 @@
+40\. Combination Sum II
+
+Medium
+
+Given a collection of candidate numbers (`candidates`) and a target number (`target`), find all unique combinations in `candidates` where the candidate numbers sum to `target`.
+
+Each number in `candidates` may only be used **once** in the combination.
+
+**Note:** The solution set must not contain duplicate combinations.
+
+**Example 1:**
+
+**Input:** candidates = \[10,1,2,7,6,1,5\], target = 8
+
+**Output:**
+
+ [
+ [1,1,6],
+ [1,2,5],
+ [1,7],
+ [2,6]
+ ] 
+
+**Example 2:**
+
+**Input:** candidates = \[2,5,2,1,2\], target = 5
+
+**Output:**
+
+ [
+ [1,2,2],
+ [5]
+ ] 
+
+**Constraints:**
+
+* `1 <= candidates.length <= 100`
+* `1 <= candidates[i] <= 50`
+* `1 <= target <= 30`
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