Here is actual code in Python, using generators to avoid using too much memory. #! /usr/bin/python def parenthesized (exprs): if len(exprs) == 1: yield exprs[0] else: first_exprs = [] last_exprs = list(exprs) while 1 < len(last_exprs): first_exprs.append(last_exprs.pop(0)) for x in parenthesized(first_exprs): if 1 < len(first_exprs): x = ‘(%s)’ % x for y in parenthesized(last_exprs): if … Read more
Inefficient, but I think clear. public static string CommaQuibbling(IEnumerable<string> items) { List<String> list = new List<String>(items); if (list.Count == 0) { return “{}”; } if (list.Count == 1) { return “{” + list[0] + “}”; } String[] initial = list.GetRange(0, list.Count – 1).ToArray(); return “{” + String.Join(“, “, initial) + ” and ” + list[list.Count … Read more
Try the following from here: template <typename T, size_t N> char ( &_ArraySizeHelper( T (&array)[N] ))[N]; #define mycountof( array ) (sizeof( _ArraySizeHelper( array ) )) int testarray[10]; enum { testsize = mycountof(testarray) }; void test() { printf(“The array count is: %d\n”, testsize); } It should print out: “The array count is: 10”
If you want O(n) time and no extra memory usage (since array was specified), use the algorithm from Jon Bentley’s book, “Programming Pearls 2nd Edition”. It swaps all the elements twice. Not as fast as using linked lists but uses less memory and is conceptually simple. shiftArray( theArray, M ): size = len( theArray ) … Read more
Sounds like a standard reduce to me: Python: def excel2num(x): return reduce(lambda s,a:s*26+ord(a)-ord(‘A’)+1, x, 0) C#: int ExcelToNumber(string x) { return x.Aggregate(0, (s, c) => s * 26 + c – ‘A’ + 1 ); }
There’s a fairly well-known trick for determining whether a number is a multiple of 11, by alternately adding and subtracting its decimal digits. If the number you get at the end is a multiple of 11, then the number you started out with is also a multiple of 11: 47278 4 – 7 + 2 … Read more
A solution in C/C++: void swap(char* str, int i, int j){ char t = str[i]; str[i] = str[j]; str[j] = t; } void reverse_string(char* str, int length){ for(int i=0; i<length/2; i++){ swap(str, i, length-i-1); } } void reverse_words(char* str){ int l = strlen(str); //Reverse string reverse_string(str,strlen(str)); int p=0; //Find word boundaries and reverse word by … Read more
Under the assumption numbers less than one are not allowed and there are no duplicates, there is a simple summation identity for this – the sum of numbers from 1 to m in increments of 1 is (m * (m + 1)) / 2. You can then sum the array and use this identity. You … Read more
Statistics. The de facto standard for testing RNGs is the Diehard suite (originally available at http://stat.fsu.edu/pub/diehard). Alternatively, the Ent program provides tests that are simpler to interpret but less comprehensive. As for shuffling algorithms, use a well-known algorithm such as Fisher-Yates (a.k.a “Knuth Shuffle”). The shuffle will be uniformly random so long as the underlying … Read more
Here is the way my own SuDoKu program does it: Start with a complete, valid board (filled with 81 numbers). Make a list of all 81 cell positions and shuffle it randomly. As long as the list is not empty, take the next position from the list and remove the number from the related cell. … Read more