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A boolean value interview question

陈皓      2012-04-30 08:49:32      4,555    0

Someone asked a question on StackOverflow, he was asked an interview question. The question is : Given 3 boolean variables a, b, c, return true if at least 2 out of the 3 are true. He gave the solution as follows :
`boolean` `atLeastTwo(``boolean` `a, ``boolean` `b, ``boolean` `c) {`
`    ``if` `((a && b) || (b && c) || (a && c)) {`
`        ``return` `true``;`
`    ``} ``else` `{`
`        ``return` `false``;`
`    ``}`
`}`

Then the interviewer asked him to improve the solution given and make it more concise. He didn't know how to improve the solution, so he posted the question on StackOverflow. There are some people who gave very useful solutions. I think this is deserved to be discussed here for us to better understand boolean values and expressions in programming. Here I share some of these solutions with you.

Some one says if you have some code snippet like
`   if` `(someExpression) {`
`       ``return` `true``;`
`   ``} ``else` `{`
`       ``return` `false``;`
`   ``}`

You should modify it as       `   return` `someExpression;`
So the solution can be improved as
`   return` `((a && b) || (b && c) || (a && c));`

Of course there are some other excellent solutions. Such as Tim Stone gave the solution
``   return a ^ b ? c : a``
Personally I think this solution is the most concise one.

Also if we use Karnaugh map, we can have

`return` `a ? (b || c) : (b && c);`If we can treat bool values a 1 or 0, then we have
`a&b | b&c | c&a``a + b + c >= 2`

If we cannot treat bool values as 1 or 0, then we have
`int` `howManyBooleansAreTrue =`
`(a ? 1 : 0)`
`+ (b ? 1 : 0)`
`+ (c ? 1 : 0);`

`return` `howManyBooleansAreTrue >= 2;`
(Shareded by danatel)

Here is one more brilliant answer
``(a==b) ? a : c;``
Want to try yourself? Put your answer here.

Author :  Source : http://coolshell.cn/articles/2514.html Original source : http://stackoverflow.com/questions/3076078/check-if-at-least-2-out-of-3-booleans-is-true/