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    <p>If we assume that the start and end ranges will follow the same alternating pattern, and limit the range of digits to <code>0-9</code> and <code>A-Z</code>, we can think of each group of digits as a component in a multi-dimensonal coordinate. For example, <code>1A</code> would correspond to the two-dimensional coordinate <code>(1,A)</code> (which is what Excel uses to label its two-dimensional grid of rows and columns); whereas <code>AA1BB2</code> would be a four-dimensional coordinate <code>(AA,1,BB,2)</code>.</p> <p>Because each component is independent, to expand the range between two coordinates we just return all combinations of the expansion of each component. Below is a quick implementation I cooked up this afternoon. It works for an arbitrary number of alternations of normal and alphabetic numbers, and handles large alphabetic ranges (i.e. from <code>AB</code> to <code>CDE</code>, not just <code>AB</code> to <code>CD</code>).</p> <p><strong>Note:</strong> This is intended as a rough draft of an actual implementation (I'm taking off tomorrow, so it is even less polished than usual ;). All the usual caveats regarding error handling, robustness, (readability ;), etc, apply.</p> <pre><code>IEnumerable&lt;string&gt; ExpandRange( string start, string end ) { // Split coordinates into component parts. string[] startParts = GetRangeParts( start ); string[] endParts = GetRangeParts( end ); // Expand range between parts // (i.e. 1-&gt;3 becomes 1,2,3; A-&gt;C becomes A,B,C). int length = startParts.Length; int[] lengths = new int[length]; string[][] expandedParts = new string[length][]; for( int i = 0; i &lt; length; ++i ) { expandedParts[i] = ExpandRangeParts( startParts[i], endParts[i] ); lengths[i] = expandedParts[i].Length; } // Return all combinations of expanded parts. int[] indexes = new int[length]; do { var sb = new StringBuilder( ); for( int i = 0; i &lt; length; ++i ) { int partIndex = indexes[i]; sb.Append( expandedParts[i][partIndex] ); } yield return sb.ToString( ); } while( IncrementIndexes( indexes, lengths ) ); } readonly Regex RangeRegex = new Regex( "([0-9]*)([A-Z]*)" ); string[] GetRangeParts( string range ) { // Match all alternating digit-letter components of coordinate. var matches = RangeRegex.Matches( range ); var parts = from match in matches.Cast&lt;Match&gt;( ) from matchGroup in match.Groups.Cast&lt;Group&gt;( ).Skip( 1 ) let value = matchGroup.Value where value.Length &gt; 0 select value; return parts.ToArray( ); } string[] ExpandRangeParts( string startPart, string endPart ) { int start, end; Func&lt;int, string&gt; toString; bool isNumeric = char.IsDigit( startPart, 0 ); if( isNumeric ) { // Parse regular integers directly. start = int.Parse( startPart ); end = int.Parse( endPart ); toString = ( i ) =&gt; i.ToString( ); } else { // Convert alphabetic numbers to integers for expansion, // then convert back for display. start = AlphaNumberToInt( startPart ); end = AlphaNumberToInt( endPart ); toString = IntToAlphaNumber; } int count = end - start + 1; return Enumerable.Range( start, count ) .Select( toString ) .Where( s =&gt; s.Length &gt; 0 ) .ToArray( ); } bool IncrementIndexes( int[] indexes, int[] lengths ) { // Increment indexes from right to left (i.e. Arabic numeral order). bool carry = true; for( int i = lengths.Length; carry &amp;&amp; i &gt; 0; --i ) { int index = i - 1; int incrementedValue = (indexes[index] + 1) % lengths[index]; indexes[index] = incrementedValue; carry = (incrementedValue == 0); } return !carry; } // Alphabetic numbers are 1-based (i.e. A = 1, AA = 11, etc, mod base-26). const char AlphaDigitZero = (char)('A' - 1); const int AlphaNumberBase = 'Z' - AlphaDigitZero + 1; int AlphaNumberToInt( string number ) { int sum = 0; int place = 1; foreach( char c in number.Cast&lt;char&gt;( ).Reverse( ) ) { int digit = c - AlphaDigitZero; sum += digit * place; place *= AlphaNumberBase; } return sum; } string IntToAlphaNumber( int number ) { List&lt;char&gt; digits = new List&lt;char&gt;( ); while( number &gt; 0 ) { int digit = number % AlphaNumberBase; if( digit == 0 ) // Compensate for 1-based alphabetic numbers. return ""; char c = (char)(AlphaDigitZero + digit); digits.Add( c ); number /= AlphaNumberBase; } digits.Reverse( ); return new string( digits.ToArray( ) ); } </code></pre>
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