Handle empty input case in Segment Tree build process

Author: roger-sato

data_structures/binary_tree/segment_tree.py

@@ -7,7 +7,8 @@ def __init__(self, a):
         self.st = [0] * (
             4 * self.N
         )  # approximate the overall size of segment tree with array N
-        self.build(1, 0, self.N - 1)
+        if self.N:
+            self.build(1, 0, self.N - 1)
 
     def left(self, idx):
         return idx * 2