"""
find_nth_set_bit32:
-------------------
Given:
- x : a 32-bit integer
- n : which set bit to find (1-based index)
Returns:
A 32-bit mask with ONLY the Nth set bit of x turned on.
If n is larger than the number of set bits, returns 0.
Algorithm:
- Use count_trailing_zeros(x) to locate the lowest set bit.
- Remove that bit using x &= (x - 1).
- When we reach the Nth one, return 1 << index.
"""
def count_trailing_zeros(x: int) -> int:
"""
Count trailing zeros in a 32-bit integer.
Equivalent to C++ std::countr_zero or GCC __builtin_ctz.
Algorithm:
- Isolate lowest set bit: x & -x
- Its index is the bit_length of that isolated bit minus 1
"""
lowest_bit = x & -x
return lowest_bit.bit_length() - 1
def find_nth_set_bit32(x: int, n: int) -> int:
"""
Find the Nth set bit (1-based) in a 32-bit integer.
Returns a mask with ONLY that bit set, or 0 if not enough bits.
"""
while x != 0:
# Index (0–31) of the lowest set bit
index = count_trailing_zeros(x)
# If this is the Nth set bit, return mask
n -= 1
if n == 0:
return 1 << index
# Remove the lowest set bit
x &= (x - 1)
# Fewer than n set bits
return 0
def to_binary32(x: int) -> str:
"""Convert integer to a padded 32-bit binary string."""
s = bin(x)[2:]
return s.zfill(32)
def main():
value = 0b00001101001101101100100010100000
n = 4
result = find_nth_set_bit32(value, n)
print("Input value: ", to_binary32(value))
print("N =", n)
print("Result mask: ", to_binary32(result))
if __name__ == "__main__":
main()
"""
run:
Input value: 00001101001101101100100010100000
N = 4
Result mask: 00000000000000000100000000000000
"""
