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Huerte merged 1 commit into from
Nov 10, 2026
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docs: add plain-English explanation to practice10 #229

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6 changes: 6 additions & 0 deletions solutions/python/practice10.py
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,12 @@
# - Input: "abccbaacz" → Output: "c" (first appears at index 2, then again at index 3)
# - Input: "abcdd" → Output: "d" (first appears at index 3, then again at index 4)
#
# Explanation (plain English):
# We read the string one letter at a time and keep a "seen" box of letters.
# For each letter, we check the box. If the letter is already there, it is
# the first one to repeat, so we return it. If not, we put it in the box.
# If we reach the end with no repeat, we return None.
#
# Status: ✅ SOLVED

def first_letter_twice(s):
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