Added tasks 6-1143

Author: javadev

Diff for: README.md

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+[![](https://img.shields.io/github/stars/LeetCode-in-Elixir/LeetCode-in-Elixir?label=Stars&style=flat-square)](https://github.com/LeetCode-in-Elixir/LeetCode-in-Elixir)
+[![](https://img.shields.io/github/forks/LeetCode-in-Elixir/LeetCode-in-Elixir?label=Fork%20me%20on%20GitHub%20&style=flat-square)](https://github.com/LeetCode-in-Elixir/LeetCode-in-Elixir/fork)
+
+## 6\. Zigzag Conversion
+
+Medium
+
+The string `"PAYPALISHIRING"` is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)
+
+P A H N A P L S I I G Y I R 
+
+And then read line by line: `"PAHNAPLSIIGYIR"`
+
+Write the code that will take a string and make this conversion given a number of rows:
+
+string convert(string s, int numRows); 
+
+**Example 1:**
+
+**Input:** s = "PAYPALISHIRING", numRows = 3
+
+**Output:** "PAHNAPLSIIGYIR" 
+
+**Example 2:**
+
+**Input:** s = "PAYPALISHIRING", numRows = 4
+
+**Output:** "PINALSIGYAHRPI"
+
+**Explanation:** P I N A L S I G Y A H R P I 
+
+**Example 3:**
+
+**Input:** s = "A", numRows = 1
+
+**Output:** "A" 
+
+**Constraints:**
+
+*   `1 <= s.length <= 1000`
+*   `s` consists of English letters (lower-case and upper-case), `','` and `'.'`.
+*   `1 <= numRows <= 1000`
+
+## Solution
+
+```elixir
+defmodule Solution do
+  @spec convert(s :: String.t, num_rows :: integer) :: String.t
+  def convert(s, 1), do: s
+  def convert(s, num_rows) do
+    String.codepoints(s)
+    |> read(%{}, 0, 1, num_rows)
+    |> then(fn map ->
+      Enum.flat_map(0..num_rows - 1, fn i ->
+        Map.get(map, i, [])
+        |> Enum.reverse()
+      end)
+    end)
+    |> to_string()
+  end
+
+  defp read([], map, _, _, _), do: map
+  defp read(s, map, -1, _, num_rows) do
+    read(s, map, 1, 1, num_rows)
+  end
+  defp read(s, map, num_rows, _, num_rows) do
+    read(s, map, num_rows - 2, -1, num_rows)
+  end
+  defp read([ch | s], map, i, add, num_rows) do
+    map = Map.update(map, i, [ch], &([ch | &1]))
+    read(s, map, i + add, add, num_rows)
+  end
+end
+```

Diff for: src/main/elixir/g0001_0100/s0006_zigzag_conversion/readme.md

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+[![](https://img.shields.io/github/stars/LeetCode-in-Elixir/LeetCode-in-Elixir?label=Stars&style=flat-square)](https://github.com/LeetCode-in-Elixir/LeetCode-in-Elixir)
+[![](https://img.shields.io/github/forks/LeetCode-in-Elixir/LeetCode-in-Elixir?label=Fork%20me%20on%20GitHub%20&style=flat-square)](https://github.com/LeetCode-in-Elixir/LeetCode-in-Elixir/fork)
+
+## 7\. Reverse Integer
+
+Medium
+
+Given a signed 32-bit integer `x`, return `x` _with its digits reversed_. If reversing `x` causes the value to go outside the signed 32-bit integer range <code>[-2<sup>31</sup>, 2<sup>31</sup> - 1]</code>, then return `0`.
+
+**Assume the environment does not allow you to store 64-bit integers (signed or unsigned).**
+
+**Example 1:**
+
+**Input:** x = 123
+
+**Output:** 321 
+
+**Example 2:**
+
+**Input:** x = -123
+
+**Output:** -321 
+
+**Example 3:**
+
+**Input:** x = 120
+
+**Output:** 21 
+
+**Example 4:**
+
+**Input:** x = 0
+
+**Output:** 0 
+
+**Constraints:**
+
+*   <code>-2<sup>31</sup> <= x <= 2<sup>31</sup> - 1</code>
+
+## Solution
+
+```elixir
+defmodule Solution do
+  @spec reverse(x :: integer) :: integer
+  def reverse(x) do
+    rev = reverse_digits(x, 0)
+    if rev > :math.pow(2, 31) - 1 or rev < -(:math.pow(2, 31)) do
+      0
+    else
+      rev
+    end
+  end
+
+  defp reverse_digits(0, acc), do: acc
+
+  defp reverse_digits(x, acc) do
+    new_acc = (acc * 10) + rem(x, 10)
+    reverse_digits(div(x, 10), new_acc)
+  end
+end
+```

Diff for: src/main/elixir/g0001_0100/s0007_reverse_integer/readme.md

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+[![](https://img.shields.io/github/stars/LeetCode-in-Elixir/LeetCode-in-Elixir?label=Stars&style=flat-square)](https://github.com/LeetCode-in-Elixir/LeetCode-in-Elixir)
+[![](https://img.shields.io/github/forks/LeetCode-in-Elixir/LeetCode-in-Elixir?label=Fork%20me%20on%20GitHub%20&style=flat-square)](https://github.com/LeetCode-in-Elixir/LeetCode-in-Elixir/fork)
+
+## 8\. String to Integer (atoi)
+
+Medium
+
+Implement the `myAtoi(string s)` function, which converts a string to a 32-bit signed integer (similar to C/C++'s `atoi` function).
+
+The algorithm for `myAtoi(string s)` is as follows:
+
+1.  Read in and ignore any leading whitespace.
+2.  Check if the next character (if not already at the end of the string) is `'-'` or `'+'`. Read this character in if it is either. This determines if the final result is negative or positive respectively. Assume the result is positive if neither is present.
+3.  Read in next the characters until the next non-digit character or the end of the input is reached. The rest of the string is ignored.
+4.  Convert these digits into an integer (i.e. `"123" -> 123`, `"0032" -> 32`). If no digits were read, then the integer is `0`. Change the sign as necessary (from step 2).
+5.  If the integer is out of the 32-bit signed integer range <code>[-2<sup>31</sup>, 2<sup>31</sup> - 1]</code>, then clamp the integer so that it remains in the range. Specifically, integers less than <code>-2<sup>31</sup></code> should be clamped to <code>-2<sup>31</sup></code>, and integers greater than <code>2<sup>31</sup> - 1</code> should be clamped to <code>2<sup>31</sup> - 1</code>.
+6.  Return the integer as the final result.
+
+**Note:**
+
+*   Only the space character `' '` is considered a whitespace character.
+*   **Do not ignore** any characters other than the leading whitespace or the rest of the string after the digits.
+
+**Example 1:**
+
+**Input:** s = "42"
+
+**Output:** 42
+
+**Explanation:** The underlined characters are what is read in, the caret is the current reader position.
+
+    Step 1: "42" (no characters read because there is no leading whitespace)
+             ^ 
+    Step 2: "42" (no characters read because there is neither a '-' nor '+')
+             ^
+    Step 3: "42" ("42" is read in)
+               ^
+
+The parsed integer is 42. Since 42 is in the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is 42. 
+
+**Example 2:**
+
+**Input:** s = " -42"
+
+**Output:** -42
+
+**Explanation:**
+
+    Step 1: " -42" (leading whitespace is read and ignored)
+              ^ 
+    Step 2: " -42" ('-' is read, so the result should be negative)
+               ^
+    Step 3: " -42" ("42" is read in)
+                 ^
+    The parsed integer is -42.
+
+Since -42 is in the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is -42. 
+
+**Example 3:**
+
+**Input:** s = "4193 with words"
+
+**Output:** 4193
+
+**Explanation:**
+
+    Step 1: "4193 with words" (no characters read because there is no leading whitespace)
+             ^
+    Step 2: "4193 with words" (no characters read because there is neither a '-' nor '+')
+             ^
+    Step 3: "4193 with words" ("4193" is read in; reading stops because the next character is a non-digit)
+                 ^ 
+    The parsed integer is 4193.
+
+Since 4193 is in the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is 4193. 
+
+**Example 4:**
+
+**Input:** s = "words and 987"
+
+**Output:** 0
+
+**Explanation:**
+
+    Step 1: "words and 987" (no characters read because there is no leading whitespace)
+             ^
+    Step 2: "words and 987" (no characters read because there is neither a '-' nor '+')
+             ^
+    Step 3: "words and 987" (reading stops immediately because there is a non-digit 'w')
+             ^
+    The parsed integer is 0 because no digits were read.
+
+Since 0 is in the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is 0. 
+
+**Example 5:**
+
+**Input:** s = "-91283472332"
+
+**Output:** -2147483648
+
+**Explanation:**
+
+    Step 1: "-91283472332" (no characters read because there is no leading whitespace)
+            ^
+    Step 2: "-91283472332" ('-' is read, so the result should be negative)
+              ^
+    Step 3: "-91283472332" ("91283472332" is read in)
+                         ^
+    The parsed integer is -91283472332.
+
+Since -91283472332 is less than the lower bound of the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is clamped to -2<sup>31</sup> = -2147483648.  
+
+**Constraints:**
+
+*   `0 <= s.length <= 200`
+*   `s` consists of English letters (lower-case and upper-case), digits (`0-9`), `' '`, `'+'`, `'-'`, and `'.'`.
+
+## Solution
+
+```elixir
+defmodule Solution do
+  @spec my_atoi(s :: String.t) :: integer
+  def my_atoi(s) do
+    result = s
+          |> String.trim
+          |> String.split
+          |> List.first
+
+    if result != nil and Integer.parse(result) != :error do
+      {num,_} = Integer.parse(result)
+      cond do
+        num < -2 ** 31 -> -2 ** 31
+        num > 2 ** 31 - 1 -> 2 ** 31 - 1
+        true  -> num
+      end
+    else
+      0
+    end
+  end
+
+end
+```

Diff for: src/main/elixir/g0001_0100/s0008_string_to_integer_atoi/readme.md

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+[![](https://img.shields.io/github/stars/LeetCode-in-Elixir/LeetCode-in-Elixir?label=Stars&style=flat-square)](https://github.com/LeetCode-in-Elixir/LeetCode-in-Elixir)
+[![](https://img.shields.io/github/forks/LeetCode-in-Elixir/LeetCode-in-Elixir?label=Fork%20me%20on%20GitHub%20&style=flat-square)](https://github.com/LeetCode-in-Elixir/LeetCode-in-Elixir/fork)
+
+## 9\. Palindrome Number
+
+Easy
+
+Given an integer `x`, return `true` if `x` is palindrome integer.
+
+An integer is a **palindrome** when it reads the same backward as forward. For example, `121` is palindrome while `123` is not.
+
+**Example 1:**
+
+**Input:** x = 121
+
+**Output:** true 
+
+**Example 2:**
+
+**Input:** x = -121
+
+**Output:** false
+
+**Explanation:** From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome. 
+
+**Example 3:**
+
+**Input:** x = 10
+
+**Output:** false
+
+**Explanation:** Reads 01 from right to left. Therefore it is not a palindrome. 
+
+**Example 4:**
+
+**Input:** x = -101
+
+**Output:** false 
+
+**Constraints:**
+
+*   <code>-2<sup>31</sup> <= x <= 2<sup>31</sup> - 1</code>
+
+**Follow up:** Could you solve it without converting the integer to a string?
+
+## Solution
+
+```elixir
+defmodule Solution do
+  @spec is_palindrome(x :: integer) :: boolean
+  def is_palindrome(x) when x < 0, do: false
+  def is_palindrome(x) when x < 10, do: true
+  def is_palindrome(x) do
+    reversed = x
+    |> Integer.digits
+    |> Enum.reverse
+    |> Integer.undigits
+
+    x == reversed
+  end
+end
+```