solves zigzag conversion

Author: anishLearnsToCode

Diff for: README.md

@@ -15,6 +15,7 @@
 |  2   | [Add Two Numbers](https://leetcode.com/problems/add-two-numbers)                                                                                          |                                                                  [![Java](assets/java.png)](src/AddTwoNumbers.java)                                                                  |                                                                                                                                   |
 |  3   | [Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters)                            |                                                   [![Java](assets/java.png)](src/LongestSubstringWithoutRepeatingCharacters.java)                                                    |                                                                                                                                   |
 |  5   | [Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring)                                                              |                                                           [![Java](assets/java.png)](src/LongestPalindromicSubstring.java)                                                           |                                                                                                                                   |
+|  6   | [Zigzag Conversion](https://leetcode.com/problems/zigzag-conversion)                                                                                      |                                                                [![Java](assets/java.png)](src/ZigZagConversion.java)                                                                 |                                                                                                                                   |
 |  7   | [Reverse Integer](https://leetcode.com/problems/reverse-integer/)                                                                                         |                                    [![Java](assets/java.png)](src/ReverseInteger.java) [![Python](assets/python.png)](python/reverse_integer.py)                                     | [![java-yt](assets/java-yt.png)](https://youtu.be/7bOhyl5lWjI) [![python-yt](assets/python-yt.png)](https://youtu.be/lmLG30TLcSg) |
 |  9   | [PalindromeNumber](https://leetcode.com/problems/palindrome-number/)                                                                                      |                                  [![Java](assets/java.png)](src/PalindromeNumber.java) [![Python](assets/python.png)](python/palindrome_number.py)                                   |                                                                                                                                   |
 |  13  | [Roman To Integer](https://leetcode.com/problems/roman-to-integer/)                                                                                       |                                    [![Java](assets/java.png)](src/RomanToInteger.java) [![Python](assets/python.png)](python/roman_to_integer.py)                                    | [![java-yt](assets/java-yt.png)](https://youtu.be/BCue_mO_81A) [![python-yt](assets/python-yt.png)](https://youtu.be/8h_yGTNvKMA) |

Diff for: src/ZigZagConversion.java

@@ -0,0 +1,31 @@
+// https://leetcode.com/problems/zigzag-conversion
+// T: O(|s|)
+// S: O(|s|)
+
+public class ZigZagConversion {
+    public static String convert(String s, int numRows) {
+        if (numRows == 1) return s;
+        final StringBuilder result = new StringBuilder();
+        final int jumpSize = (numRows - 1) * 2;
+
+        // first row
+        for (int i = 0 ; i < s.length() ; i += jumpSize) {
+            result.append(s.charAt(i));
+        }
+
+        for (int row = 1 ; row < numRows - 1 ; row++) {
+            int[] jumps = {jumpSize - 2 * row, 2 * row};
+            for (int i = row, k = 0 ; i < s.length() ; k ^= 1) {
+                result.append(s.charAt(i));
+                i += jumps[k];
+            }
+        }
+
+        // last row
+        for (int i = numRows - 1 ; i < s.length() ; i += jumpSize) {
+            result.append(s.charAt(i));
+        }
+
+        return result.toString();
+    }
+}