Log convert_base attempt (solved with hints, optimal) and add flashcards

Author: Brian Elinsky

problem-questions/06_strings/6.02_convert_base/00_key_insight.md

@@ -0,0 +1,9 @@
+# Key Insight
+
+**Q:** What's the key insight for converting between arbitrary bases?
+
+**A:** Use decimal (Python's integer type) as an intermediate representation. Convert b1 → int → b2.
+
+```
+"615" (base 7)  →  306 (decimal)  →  "1A7" (base 13)
+```

problem-questions/06_strings/6.02_convert_base/01_two_phases.md

@@ -0,0 +1,9 @@
+# Two Phases of Conversion
+
+**Q:** What are the two main phases of base conversion?
+
+**A:**
+1. **String → Int:** Parse the string in base b1 to get decimal integer
+2. **Int → String:** Convert the integer to a string in base b2
+
+Note: There's no separate "number in base N" - the string IS the base-N representation. Parsing directly produces the int; formatting directly produces the string.

problem-questions/06_strings/6.02_convert_base/02_string_to_int_formula.md

@@ -0,0 +1,5 @@
+# String to Int Formula
+
+**Q:** What's the formula to convert a string "d2 d1 d0" in base b to an integer?
+
+**A:** `result = d2 * b^2 + d1 * b^1 + d0 * b^0`

problem-questions/06_strings/6.02_convert_base/03_char_to_digit.md

@@ -0,0 +1,5 @@
+# Character to Digit Value
+
+**Q:** How do you convert a single character ('0'-'9', 'A'-'F') to its digit value?
+
+**A:** `string.hexdigits.index(c.lower())` — returns 0-15

problem-questions/06_strings/6.02_convert_base/04_digit_position_meaning.md

@@ -0,0 +1,5 @@
+# Digit Position Meaning
+
+**Q:** In base b, what does each digit position represent (right to left)?
+
+**A:** Powers of b: rightmost is b^0, then b^1, b^2, ...

problem-questions/06_strings/6.02_convert_base/05_base7_example.md

@@ -0,0 +1,5 @@
+# Base 7 Example
+
+**Q:** What does "61" in base 7 mean in decimal?
+
+**A:** `6 * 7^1 + 1 * 7^0 = 42 + 1 = 43`

problem-questions/06_strings/6.02_convert_base/06_hex_example.md

@@ -0,0 +1,5 @@
+# Hex Example
+
+**Q:** What does "1A" in base 16 mean in decimal?
+
+**A:** `1 * 16^1 + 10 * 16^0 = 16 + 10 = 26`

problem-questions/06_strings/6.02_convert_base/07_accumulation_pattern.md

@@ -0,0 +1,7 @@
+# Accumulation Pattern
+
+**Q:** What's the accumulation pattern for building an integer from digits (left to right)?
+
+**A:**
+1. Shift left: `result = result * base`
+2. Add digit: `result = result + digit`

problem-questions/06_strings/6.02_convert_base/08_string_to_int_algorithm.md

@@ -0,0 +1,11 @@
+# String to Int Algorithm
+
+**Q:** Describe the algorithm to convert a string in base b to a base 10 int.
+
+**A:**
+1. Start with result = 0
+2. For each character left to right:
+   - Convert character (base b) to digit value (base 10) using hexdigits lookup
+   - Shift result left (multiply by base)
+   - Add digit to result
+3. Return result

problem-questions/06_strings/6.02_convert_base/09_extract_digits_operations.md

@@ -0,0 +1,7 @@
+# Extract Digits Operations
+
+**Q:** What two operations extract digits when converting a base 10 int to base b?
+
+**A:**
+- `num % base` → gives the least significant digit (rightmost)
+- `num // base` → removes the least significant digit