Question

I have some int value its name is number. I have other int value its name is x. I want to know is x exist in number or not. Currently I convert number to string() and use string.Contain(x) method. I think this is not a good way, it does boxing and performance is hurt.

Are there a better way to do this?

Additional information:
number may be one or more digit, for example, 12345. x is always one digit.

Answer 1

That’s not a bad method. The only alternative I can think of is something using repeated divisions and modulus operators which may well be slower due to the quantity of those operations.

I’d stick with what you have unless there’s a serious performance problem.

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Based on your additional information:

number may be one or more digit, for example, 12345. x is always one digit.

I would opt for the following (pseudo-code):

def numContains (number, digit):
    if number == 0 and digit == 0:
        return true
    while number != 0:
        if number % 10 == digit:
            return true
        number = number / 10
    return false

The first if is required since you don’t enter the while if you pass in a number of 0 and you still have to catch the case where both number and digit are 0.

Otherwise, you just continue to check the least significant digit of number against digit, and divide number by 10 each time.

If a match is found before number reaches zero, it contains the digit. Otherwise it doesn’t.

This will probably be faster than your string solution, since it will have to do similar operations to create the string from the integer and then do the string compare on top of that.

But, as with all optimisations, measure, don’t guess!

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And, now that I have access to my VS2008 development box, her’s some C# code for it:

// Function: containsDigit, returns whether non-negative number holds a digit.
//       In: num, the integer to check.
//           dgt, the digit to look for.
//      Out: Boolean representing whether digit found in number.
//    Notes: Digit is coerced to a single digit.

Boolean containsDigit(UInt32 num, UInt32 dgt) {
    dgt = dgt % 10;                // silently force contract compliance.
    if ((num == 0) && (dgt == 0))  // Zero contains zero.
        return true;
    while (num != 0) {             // While more digits in number.
        if ((num % 10) == dgt)     // Return true if rightmost digit matches.
            return true;
        num = num / 10;            // Get next digit into rightmost position.
    }
    return false;                  // No matches, return false.
}