diff options
Diffstat (limited to 'libphobos/src/std/algorithm')
| -rw-r--r-- | libphobos/src/std/algorithm/searching.d | 131 |
1 files changed, 129 insertions, 2 deletions
diff --git a/libphobos/src/std/algorithm/searching.d b/libphobos/src/std/algorithm/searching.d index e0d2435..924ea1c 100644 --- a/libphobos/src/std/algorithm/searching.d +++ b/libphobos/src/std/algorithm/searching.d @@ -34,6 +34,7 @@ $(T2 commonPrefix, `commonPrefix("parakeet", "parachute")` returns `"para"`.) $(T2 endsWith, `endsWith("rocks", "ks")` returns `true`.) +$(T2 extrema, `extrema([2, 1, 3, 5, 4])` returns `[1, 5]`.) $(T2 find, `find("hello world", "or")` returns `"orld"` using linear search. (For binary search refer to $(REF SortedRange, std,range).)) @@ -3684,7 +3685,7 @@ Note: See_Also: - $(LREF maxElement), $(REF min, std,algorithm,comparison), $(LREF minCount), + $(LREF extrema), $(LREF maxElement), $(REF min, std,algorithm,comparison), $(LREF minCount), $(LREF minIndex), $(LREF minPos) */ auto minElement(alias map = (a => a), Range)(Range r) @@ -3865,7 +3866,7 @@ Note: See_Also: - $(LREF minElement), $(REF max, std,algorithm,comparison), $(LREF maxCount), + $(LREF extrema), $(LREF minElement), $(REF max, std,algorithm,comparison), $(LREF maxCount), $(LREF maxIndex), $(LREF maxPos) */ auto maxElement(alias map = (a => a), Range)(Range r) @@ -4035,6 +4036,132 @@ if (isInputRange!Range && !isInfinite!Range && assert(maxElement(arr) == S(145)); } +/** Returns an array of the minimum and maximum element in `r`. + * Performs `< 3n/2` comparisons, unlike the naive `< 2n`. + * Params: + * r = The range to traverse. + */ +// TODO alias map = a => a +ElementType!Range[2] extrema(Range)(Range r) +if (isInputRange!Range && !isInfinite!Range) +in (!r.empty) +{ + static if (isRandomAccessRange!Range && hasLength!Range) + { + if (r.length == 1) + return [r[0], r[0]]; + + typeof(return) result; + size_t i; + if (r.length & 1) // odd + { + result = [r[0], r[0]]; + i = 1; + } + else + { + result = (r[0] < r[1]) ? [r[0], r[1]] : [r[1], r[0]]; + i = 2; + } + // iterate pairs + const imax = r.length; + for (; i != imax; i += 2) + { + // save work + if (r[i] < r[i+1]) + { + if (r[i] < result[0]) + result[0] = r[i]; + if (r[i+1] > result[1]) + result[1] = r[i+1]; + } + else + { + if (r[i+1] < result[0]) + result[0] = r[i+1]; + if (r[i] > result[1]) + result[1] = r[i]; + } + } + return result; + } + else + { + auto first = r.front; + r.popFront; + if (r.empty) + return [first, first]; + + typeof(return) result = (first < r.front) ? [first, r.front] : [r.front, first]; + // iterate pairs + while (true) + { + r.popFront; + if (r.empty) + return result; + first = r.front; + r.popFront; + if (r.empty) + { + if (first < result[0]) + result[0] = first; + else if (first > result[1]) + result[1] = first; + return result; + } + // save work + if (first < r.front) + { + if (first < result[0]) + result[0] = first; + if (r.front > result[1]) + result[1] = r.front; + } + else + { + if (r.front < result[0]) + result[0] = r.front; + if (first > result[1]) + result[1] = first; + } + } + } +} + +/// +@safe unittest +{ + assert(extrema([5,2,9,4,1]) == [1, 9]); +} + +@safe unittest +{ + assert(extrema([8,3,7,4,9]) == [3, 9]); + assert(extrema([1,5,3,2]) == [1, 5]); + assert(extrema([2,3,3,2]) == [2, 3]); + + import std.range; + assert(iota(2, 5).extrema == [2, 4]); + assert(iota(3, 7).retro.extrema == [3, 6]); + + import std.internal.test.dummyrange; + foreach (DummyType; AllDummyRanges) + { + DummyType d; + assert(d.extrema == [1, 10]); + } + + version (StdRandomTests) + foreach (i; 0 .. 1000) + { + import std.random; + auto arr = generate!(() => uniform(0, 100)).takeExactly(uniform(1, 10)).array; + auto result = arr.extrema; + assert(result[0] == arr.minElement); + assert(result[1] == arr.maxElement); + } +} + // minPos /** Computes a subrange of `range` starting at the first occurrence of `range`'s |