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#
# You are given an integer $N.
#
# Write a script to reverse the given integer and print the result.
# Print 0 if the result doesn't fit in 32-bit signed integer.
#
# The number 2,147,483,647 is the maximum positive value for a 32-bit
# signed binary integer in computing.
#
#
# This is two challenges in one. First, we have to reverse a given
# integer -- which in AWK we do character by character.
#
# For the second part, we have to compare it against a given
# maximum value. Awk, or at least my version, handles big integers
# just fine.
#
# There's a tiny thing to consider. 2,147,483,647 is the largest
# positive value which fits in a 32-bit signed integer, but the
# smallest integer which fits is -2,147,483,648 [1]. So, if the input
# is 8463847412, the output should 0, but if the input is -8463847412,
# the output should be -2147483648.
#
# [1] We're assuming 2s-complement integers, which seems to have
# been the norm for the past 50 years or so.
#
{
low = 0; # Indicates lower bound for reversing
reverse = ""; # This will contain the reversed number.
#
# Check whether the number starts with a hyphen; if so,
# keep the sign, and don't include it in the part which
# needs reversing.
#
if (substr ($0, 1, 1) == "-") {
reverse = "-";
low = 1;
}
#
# Do the actual reversal. Note that in AWK strings are 1-based,
# and, hence, length() gives the highest index.
#
for (i = length ($0); i > low; i --) {
reverse = reverse substr ($0, i, 1);
}
#
# Turn reverse into a number
#
reverse = reverse + 0;
#
# Check wether it fits in a 32-bit integer (we assume 2's complement)
#
if (reverse < -2147483648 || reverse > 2147483647) {
reverse = 0;
}
print reverse;
}
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