Add ZigZag Conversion

LeetCode/Problems/Python/ZigZag Conversion/ZigZag Conversion.py

@@ -0,0 +1,16 @@
+class Solution:
+    def convert(self, s: str, numRows: int) -> str:
+        if numRows < 2:
+            return s
+        i = 0
+        res = [""]*numRows      # We will fill in each line in the zigzag
+        for letter in s:
+            if i == numRows-1:  # If this is the last line in the zigzag we go up
+                grow = False
+            elif i == 0:        #Otherwise we go down
+                grow = True 
+            res[i] += letter    #Add the letter to its row
+            i = (i+1) if grow else i-1  # We increment (add 1) if grow is True, 
+			                            # and decrement otherwise
+
+        return "".join(res)     # return the joined rows