8/17/23 - slow day

I think I'm going to switch to focusing on just Python again;
feeling like there's too much room for embarassing error when jumping
between them.

- convert_base.py

Author: jsgoller1

elements-of-programming-interviews/problem_mapping.js

@@ -504,7 +504,7 @@ problem_mapping = {
                 "total": 20001
             },
             "Python: convert_base.py": {
-                "passed": 0,
+                "passed": 20001,
                 "total": 20001
             }
         },

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

@@ -1,17 +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:
-    # TODO - you fill in here.
-    return ''
+    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)
 
-if __name__ == '__main__':
+    return ("-" if neg else "") + num_b2
 
-    assert convert_base("1234", 10, 2) == bin(1234)
 
-    """
+if __name__ == '__main__':
     exit(
         generic_test.generic_test_main('convert_base.py', 'convert_base.tsv',
                                        convert_base))
-    """