import std.array; import std.stdio; import std.string; import std.range; import std.algorithm; struct FibonacciSeries { int first = 0; int second = 1; enum empty = false; // infinite range @property int front() const { return first; } void popFront() { int third = first + second; first = second; second = third; } @property FibonacciSeries save() const { return this; } } void report(T)(const dchar[] title, const ref T range) { writefln("%40s: %s", title, range.take(5)); } class SquaresRange { int first; this(int first = 0) { this.first = first; } enum empty = false; @property int front() const { return opIndex(0); } void popFront() { ++first; } @property SquaresRange save() const { return new SquaresRange(first); } int opIndex(size_t index) const { /* This function operates at constant time */ immutable integerValue = first + cast(int)index; return integerValue * integerValue; } } bool are_lastTwoDigitsSame(int value) { /* Must have at least two digits */ if (value < 10) { return false; } /* Last two digits must be divisible by 11 */ immutable lastTwoDigits = value % 100; return (lastTwoDigits % 11) == 0; } struct Together { const(int)[][] slices; this(const(int)[][] slices ...) { this.slices = slices.dup; clearFront(); clearBack(); } private void clearFront() { while (!slices.empty && slices.front.empty) { slices.popFront(); } } private void clearBack() { while (!slices.empty && slices.back.empty) { slices.popBack(); } } @property bool empty() const { return slices.empty; } @property int front() const { return slices.front.front; } void popFront() { slices.front.popFront(); clearFront(); } @property Together save() const { return Together(slices.dup); } @property int back() const { return slices.back.back; } void popBack() { slices.back.popBack(); clearBack(); } @property size_t length() const { return reduce!((a, b) => a + b.length)(size_t.init, slices); } int opIndex(size_t index) const { /* Save the index for the error message */ immutable originalIndex = index; foreach (slice; slices) { if (slice.length > index) { return slice[index]; } else { index -= slice.length; } } throw new Exception( format("Invalid index: %s (length: %s)", originalIndex, this.length)); } } void main() { auto range = Together(FibonacciSeries().take(10).array, [ 777, 888 ], (new SquaresRange()).take(5).array); writeln(range.save); }
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