Comments on Lone ones
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Lone ones
Given an integer, output the number of lone 1s in its binary representation.
Input
- An integer from $0$ to $4294967295$ (that is, $2^{32}-1$). In binary that's from
00000000000000000000000000000000to11111111111111111111111111111111. - You may take input in any form that does not contribute to solving the challenge. For example:
- A signed or unsigned integer of $32$ bits or more.
- A string of decimal digits.
- A binary string.
- A sequence of bits.
Output
- The number of
1s in the binary representation that do not have a1to their left or right. - For avoidance of doubt:
- A
1at the left end of the binary representation does not have a1to its left. - A
1at the right end of the binary representation does not have a1to its right.
- A
Examples
Input $4$ corresponds to 100 in binary. The output is $1$ because there is $1$ 1 bit that is not adjacent to another 1 bit.
Input $5$ corresponds to 101 in binary. The output is $2$ because there are $2$ 1 bits that are not adjacent to another 1 bit.
Input $6$ corresponds to 110 in binary. The output is $0$ because each of the 1 bits is adjacent to another 1 bit.
Test cases
Test cases are in the format input : output.
Unsigned integer test cases
0 : 0
4294967295 : 0
2147483648 : 1
1 : 1
2147483649 : 2
98304 : 0
1310720 : 2
4294639615 : 1
4294967294 : 0
2147483647 : 0
3221225471 : 1
4294967293 : 1
2863311530 : 16
1431655765 : 16
1717986918 : 0
Binary test cases
00000000000000000000000000000000 : 0
11111111111111111111111111111111 : 0
10000000000000000000000000000000 : 1
00000000000000000000000000000001 : 1
10000000000000000000000000000001 : 2
00000000000000011000000000000000 : 0
00000000000101000000000000000000 : 2
11111111111110101111111111111111 : 1
11111111111111111111111111111110 : 0
01111111111111111111111111111111 : 0
10111111111111111111111111111111 : 1
11111111111111111111111111111101 : 1
10101010101010101010101010101010 : 16
01010101010101010101010101010101 : 16
01100110011001100110011001100110 : 0
Scoring
This is a code golf challenge. Your score is the number of bytes in your code. Lowest score for each language wins.
Explanations are optional, but I'm more likely to upvote answers that have one.
awk, 35 bytes Takes input …
7mo ago
[C (gcc)], 67 bytes …
7mo ago
Bash, 53 bytes ``` sed 's/ …
7mo ago
Vyxal, 4 bytes ``` Ġċ†∑ …
7mo ago
Japt `-x`, 4 bytes Takes in …
6mo ago
Uiua, 19 17 bytes (SBCS) Ta …
6mo ago
vim, 42 bytes Better approa …
6mo ago
vim, 77 bytes Input is a bi …
6mo ago
[C (gcc)], 44 bytes Borrowi …
7mo ago
Bash, 28 bytes Takes inpu …
7mo ago
Perl, 28 bytes Takes inpu …
7mo ago
Post
C (gcc), 67 bytes
a;r;i;f(long n){for(;i<33;)a=n&1l<<i++?a?2:1:a&1?r++,0:0;return a;}
General algorithm:
-
This is a little state machine where the variable 'alone'
acan have the value 0=zero, 1=alone candidate, 2=not alone. Essentially a 'carry' but with several states.The non-golfed code would look something like
if(!a) a=1; else a=2;which becomesa=a?2:1. -
Then the outer if-else non-golfed would look something like
if(n&1l<<i) a=a?2:1; else { if(a&1) r++; a=0; }...which turns into the one-liner
?:mess. -
When the state machine has found an alone candidate and transits from value 1 to zero, increase count
r -
Whenever there's a zero, reset the state machine.
-
To solve the special case at the end where there might be a lone 1, iterate one more than 32 times to get comparison with a zero in there. Which will only work if the function parameter is not sign extended! To cheat I used
longwhich is 64 bit on Linux that tio.run uses - won't work on 32 bitlongsystems. Making the parameter unsigned would be portable butunsignedhas more digits thanlong. Same thing with the1lprefix, which needs to be1ullto be portable.
C-specific stuff:
- Plain int is 32 bits.
- Operator precedence
++over<<over&over?:over=over,. - Shifting negative numbers is of course wildly poorly-specified behavior but the code gets away with it on gcc/Linux.
Test cases:
- Taken from the challenge. An ugly macro takes a digit and expected output, then prints OK or FAIL.
- As usual, the function-only solution relying on zero init of global variables need to be reset by the caller between tests.
- Also print test cases as hex because the decimal numbers really don't tell me much :)
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