diff --git a/project_euler/problem_112/__init__.py b/project_euler/problem_112/__init__.py
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diff --git a/project_euler/problem_112/sol1.py b/project_euler/problem_112/sol1.py
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+++ b/project_euler/problem_112/sol1.py
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+"""
+Problem 112: https://projecteuler.net/problem=112
+
+Working from left-to-right if no digit is exceeded by the digit to its left it is
+called an increasing number; for example, 134468.
+Similarly if no digit is exceeded by the digit to its right it is called a decreasing
+number; for example, 66420.
+We shall call a positive integer that is neither increasing nor decreasing a "bouncy"
+number, for example, 155349.
+Clearly there cannot be any bouncy numbers below one-hundred, but just over half of
+the numbers below one-thousand (525) are bouncy. In fact, the least number for which
+the proportion of bouncy numbers first reaches 50% is 538.
+Surprisingly, bouncy numbers become more and more common and by the time we reach
+21780 the proportion of bouncy numbers is equal to 90%.
+
+Find the least number for which the proportion of bouncy numbers is exactly 99%.
+"""
+
+
+def check_bouncy(n: int) -> bool:
+    """
+    Returns True if number is bouncy, False otherwise
+    >>> check_bouncy(6789)
+    False
+    >>> check_bouncy(-12345)
+    False
+    >>> check_bouncy(0)
+    False
+    >>> check_bouncy(6.74)
+    Traceback (most recent call last):
+        ...
+    ValueError: check_bouncy() accepts only integer arguments
+    >>> check_bouncy(132475)
+    True
+    >>> check_bouncy(34)
+    False
+    >>> check_bouncy(341)
+    True
+    >>> check_bouncy(47)
+    False
+    >>> check_bouncy(-12.54)
+    Traceback (most recent call last):
+        ...
+    ValueError: check_bouncy() accepts only integer arguments
+    >>> check_bouncy(-6548)
+    True
+    """
+    if not isinstance(n, int):
+        raise ValueError("check_bouncy() accepts only integer arguments")
+    return "".join(sorted(str(n))) != str(n) and "".join(sorted(str(n)))[::-1] != str(n)
+
+
+def solution(percent: float = 99) -> int:
+    """
+    Returns the least number for which the proportion of bouncy numbers is
+    exactly 'percent'
+    >>> solution(50)
+    538
+    >>> solution(90)
+    21780
+    >>> solution(80)
+    4770
+    >>> solution(105)
+    Traceback (most recent call last):
+        ...
+    ValueError: solution() only accepts values from 0 to 100
+    >>> solution(100.011)
+    Traceback (most recent call last):
+        ...
+    ValueError: solution() only accepts values from 0 to 100
+    """
+    if not 0 < percent < 100:
+        raise ValueError("solution() only accepts values from 0 to 100")
+    bouncy_num = 0
+    num = 1
+
+    while True:
+        if check_bouncy(num):
+            bouncy_num += 1
+        if (bouncy_num / num) * 100 >= percent:
+            return num
+        num += 1
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()
+    print(f"{solution(99)}")