8/19/23 - Clemson dropoff, trip up and back

- convert_base.py (solved recursively and iteratively)

Author: jsgoller1

elements-of-programming-interviews/python/convert_base.py

@@ -14,45 +14,33 @@
 - Ex: convert "12345" to int 12345
     - add each digit, then multiply total by 10. 
 """
+import functools
+import string
 
-# easier to read than ord()/chr()
-CHAR_AS_NUM = {str(i): i for i in range(10)} | {'A': 10, 'B': 11, 'C': 12, 'D': 13, 'E': 14, 'F': 15}
 NUM_AS_CHAR = "0123456789ABCDEF"
 
 
-def to_new_base(num: int, b2: int) -> str:
-    if num == 0:
-        return "0"
-    val = ""
-    while num:
-        remainder = num % b2
-        val = NUM_AS_CHAR[remainder] + val   # prepend the new digit
-        num //= b2
-    return val
-
-
-def to_base_ten(num_as_string: str, b1: int) -> int:
-    total = 0
-    place = 1
-    for c in num_as_string[::-1]:
-        total += (CHAR_AS_NUM[c] * place)
-        place *= b1
-    return total
-
-
 def convert_base(num_as_string: str, b1: int, b2: int) -> str:
-    if not num_as_string:
-        return ""
-    neg = num_as_string[0] == '-'
-    num_as_string = num_as_string[1:] if neg else num_as_string
+    # Assuming 2 <= b1,b2 <= 16
+    if num_as_string in ["", "0"]:
+        return num_as_string
+    neg = num_as_string[0] == "-"
+
+    num_as_int = functools.reduce(
+        lambda x, c: x * b1 + string.hexdigits.index(c.lower()),
+        num_as_string[neg:], 0)
 
-    num_base_10 = to_base_ten(num_as_string, b1)
-    num_b2 = to_new_base(num_base_10, b2)
+    def recurse(num_as_int, b2):
+        if num_as_int == 0:
+            return ""
+        remainder = num_as_int % b2
+        return recurse(num_as_int // b2, b2) + NUM_AS_CHAR[remainder]
 
-    return ("-" if neg else "") + num_b2
+    return ("-" if neg else "") + recurse(num_as_int, b2)
 
 
 if __name__ == '__main__':
+    print(convert_base("1234", 10, 5))
     exit(
         generic_test.generic_test_main('convert_base.py', 'convert_base.tsv',
                                        convert_base))

elements-of-programming-interviews/python/convert_base_with_two_fns.py

@@ -0,0 +1,58 @@
+from test_framework import generic_test
+
+"""
+- Bases can be between 2 and 16
+- Can be empty? 
+- Can exceed integer limits (not issue for python)
+- Negatives
+- num_as_string[0] is most sig fig
+- 0 and 1 are always valid; A = 10, ..., F = 15
+
+Input: string representing num in b1
+Output: string representing num in b2
+
+- Ex: convert "12345" to int 12345
+    - add each digit, then multiply total by 10. 
+"""
+
+# easier to read than ord()/chr()
+CHAR_AS_NUM = {str(i): i for i in range(10)} | {'A': 10, 'B': 11, 'C': 12, 'D': 13, 'E': 14, 'F': 15}
+NUM_AS_CHAR = "0123456789ABCDEF"
+
+
+def to_new_base(num: int, b2: int) -> str:
+    if num == 0:
+        return "0"
+    val = ""
+    while num:
+        remainder = num % b2
+        val = NUM_AS_CHAR[remainder] + val   # prepend the new digit
+        num //= b2
+    return val
+
+
+def to_base_ten(num_as_string: str, b1: int) -> int:
+    total = 0
+    place = 1
+    for c in num_as_string[::-1]:
+        total += (CHAR_AS_NUM[c] * place)
+        place *= b1
+    return total
+
+
+def convert_base(num_as_string: str, b1: int, b2: int) -> str:
+    if not num_as_string:
+        return ""
+    neg = num_as_string[0] == '-'
+    num_as_string = num_as_string[1:] if neg else num_as_string
+
+    num_base_10 = to_base_ten(num_as_string, b1)
+    num_b2 = to_new_base(num_base_10, b2)
+
+    return ("-" if neg else "") + num_b2
+
+
+if __name__ == '__main__':
+    exit(
+        generic_test.generic_test_main('convert_base.py', 'convert_base.tsv',
+                                       convert_base))