How do you identify “edge” cases on algorithms?

up vote7down votefavorite 3	Basically how do you find out which could be your worst or best case and any other "edge" cases you might have BEFORE having them and so, how do you prepare your code for them? testing algorithms knowledge-base shareimprove this question edited May 1 '11 at 11:07 Victor Hurdugaci 2,646620 asked May 1 '11 at 3:47 Luis Armando 21015

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Based on the content of the algorithm you can identify what data structures/types/constructs are used. Then, you try to understand the (possible) weak points of those and try to come up with an execution plan that will make it run in those cases. For example, the algorithm takes a string and an integer as input and does some sorting of the characters of the string. Here we have: String with some known special cases: Empty string Long string Unicode string (special characters) If limited to a specific set of characters, what happens when some are not in the range Odd/even length string Null (as argument) Non-null terminated Integer with known special cases: 0 Min/MaxInt Negative/Positive Sort algorithm that could fail in the following boundary cases: Empty input 1 element input Very long input (maybe of length max(data type used for index)) Garbage inside the collection that will be sorted Null input Duplicate elements Collection with all elements equal Odd/even length input Then, take all these cases and create a long list trying to understand how they overlap. Ex: Empty string case covers the empty collection case Null string == null collection etc. Now create test cases for them :) Short summary: break the algorithm in basic blocks for which you know the boundary cases and then reassemble them, creating global boundary cases shareimprove this answer answered May 1 '11 at 10:46 Victor Hurdugaci 2,646620