Programming-Idioms

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Idiom #124 Binary search for a value in sorted array

Write function binarySearch which returns the index of an element having value x in sorted array a, or -1 if no such element.

bsearch([], _) -> -1;
bsearch([H|_T], X) when X < H -> -1;
bsearch(List, X) -> 
  bsearch(List, X, 0, length(List)).

bsearch(_List, _X, First, Last) when Last < First -> -1;
bsearch(List, X, First, Last) -> 
  Middle = (First + Last) div 2,
  Item = lists:nth(Middle, List),
  case Item of
    X -> Middle;
    _Less when X < Item -> bsearch(List, X, First, Middle);
    _More -> bsearch(List, X, Middle + 1, Last)
  end.
import std.range;
import std.algorithm;
long binarySearch(long[] a, long x) {
    long result = a.assumeSorted.lowerBound(x).length;
    if (result == a.length || a[result] != x)
        return -1;
    return result;
}
def binarySearch(ar, el)
  res = ar.bsearch{|x| x == el}
  res ? res : -1
end
func binarySearch(a []T, x T) int {
	imin, imax := 0, len(a)-1
	for imin <= imax {
		imid := (imin + imax) / 2
		switch {
		case a[imid] == x:
			return imid
		case a[imid] < x:
			imin = imid + 1
		default:
			imax = imid - 1
		}
	}
	return -1
}
import "sort"
func binarySearch(a []int, x int) int {
	i := sort.SearchInts(a, x)
	if i < len(a) && a[i] == x {
		return i
	}
	return -1
}
import "sort"
func binarySearch(a []T, x T) int {
	f := func(i int) bool { return a[i] >= x }
	i := sort.Search(len(a), f)
	if i < len(a) && a[i] == x {
		return i
	}
	return -1
}
binSearch :: Ord a => a -> [a] -> Maybe Int
binSearch _ [] = Nothing
binSearch t l = let n = div (length l) 2
                    (a, m:b) = splitAt n l in
                if t < m then binSearch t a
                else if t > m then aux (binSearch t b)
                else Just n where
    aux :: Maybe Int -> Maybe Int
    aux (Just x) = Just (x+n+1)
    aux _ = Nothing
function binarySearch(a, x, i = 0) {
  if (a.length === 0) return -1
  const half = (a.length / 2) | 0
  return (a[half] === x) ?
    i + half :
    (a[half] > x) ?
    binarySearch(a.slice(0, half), x, i) :
    binarySearch(a.slice(half + 1), x, half + i + 1)
}
import java.util.arrays;
static int binarySearch(final int[] arr, final int key) {
    final int index = Arrays.binarySearch(arr, key);
    return index < 0 ? - 1 : index;
}
function BinarySearch(X: Integer; A: Array of Integer): Integer;
var
  L, R, I, Cur: Integer;
begin
  Result := -1;
  if Length(A) = 0 then Exit;
  L := Low(A);
  R := High(A);
  while (L <= R) do
  begin
    I := L + (R - L) div 2;
    Cur := A[I];
    if (X = Cur) then Exit(I);
    if (X > Cur) then
       L := I + 1
    else
      R := I - 1;
  end;
end;
use 5.020;
sub binary_search {
    my ($x, $A, $lo, $hi) = @_;
    $lo //= 0;
    $hi //= @$A;
    my $mid = int(($lo + $hi) / 2);
    for ($x cmp $A->[$mid]) {
        use experimental 'switch';
        return $mid when 0;
        return -1 if 1 == $hi - $lo;
        return binary_search($x, $A, $lo, $mid) when -1;
        return binary_search($x, $A, $mid, $hi) when 1;
    }
}

import bisect
def binarySearch(a, x):
    i = bisect.bisect_left(a, x)
    return i if i != len(a) and a[i] == x else -1

def binary_search(a, el)
  a.bsearch_index{|x| x == el} || -1
end
a.binary_search(&x).unwrap_or(-1);
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programming-idioms.org 
bsearch([], _) -> -1;
bsearch([H|_T], X) when X < H -> -1;
bsearch(List, X) -> 
  bsearch(List, X, 0, length(List)).

bsearch(_List, _X, First, Last) when Last < First -> -1;
bsearch(List, X, First, Last) -> 
  Middle = (First + Last) div 2,
  Item = lists:nth(Middle, List),
  case Item of
    X -> Middle;
    _Less when X < Item -> bsearch(List, X, First, Middle);
    _More -> bsearch(List, X, Middle + 1, Last)
  end.
long binarySearch(long[] a, long x) {
    long result = a.assumeSorted.lowerBound(x).length;
    if (result == a.length || a[result] != x)
        return -1;
    return result;
}
def binarySearch(ar, el)
  res = ar.bsearch{|x| x == el}
  res ? res : -1
end
func binarySearch(a []T, x T) int {
	imin, imax := 0, len(a)-1
	for imin <= imax {
		imid := (imin + imax) / 2
		switch {
		case a[imid] == x:
			return imid
		case a[imid] < x:
			imin = imid + 1
		default:
			imax = imid - 1
		}
	}
	return -1
}
func binarySearch(a []int, x int) int {
	i := sort.SearchInts(a, x)
	if i < len(a) && a[i] == x {
		return i
	}
	return -1
}
func binarySearch(a []T, x T) int {
	f := func(i int) bool { return a[i] >= x }
	i := sort.Search(len(a), f)
	if i < len(a) && a[i] == x {
		return i
	}
	return -1
}
binSearch :: Ord a => a -> [a] -> Maybe Int
binSearch _ [] = Nothing
binSearch t l = let n = div (length l) 2
                    (a, m:b) = splitAt n l in
                if t < m then binSearch t a
                else if t > m then aux (binSearch t b)
                else Just n where
    aux :: Maybe Int -> Maybe Int
    aux (Just x) = Just (x+n+1)
    aux _ = Nothing
function binarySearch(a, x, i = 0) {
  if (a.length === 0) return -1
  const half = (a.length / 2) | 0
  return (a[half] === x) ?
    i + half :
    (a[half] > x) ?
    binarySearch(a.slice(0, half), x, i) :
    binarySearch(a.slice(half + 1), x, half + i + 1)
}
static int binarySearch(final int[] arr, final int key) {
    final int index = Arrays.binarySearch(arr, key);
    return index < 0 ? - 1 : index;
}
function BinarySearch(X: Integer; A: Array of Integer): Integer;
var
  L, R, I, Cur: Integer;
begin
  Result := -1;
  if Length(A) = 0 then Exit;
  L := Low(A);
  R := High(A);
  while (L <= R) do
  begin
    I := L + (R - L) div 2;
    Cur := A[I];
    if (X = Cur) then Exit(I);
    if (X > Cur) then
       L := I + 1
    else
      R := I - 1;
  end;
end;
sub binary_search {
    my ($x, $A, $lo, $hi) = @_;
    $lo //= 0;
    $hi //= @$A;
    my $mid = int(($lo + $hi) / 2);
    for ($x cmp $A->[$mid]) {
        use experimental 'switch';
        return $mid when 0;
        return -1 if 1 == $hi - $lo;
        return binary_search($x, $A, $lo, $mid) when -1;
        return binary_search($x, $A, $mid, $hi) when 1;
    }
}

def binarySearch(a, x):
    i = bisect.bisect_left(a, x)
    return i if i != len(a) and a[i] == x else -1

def binary_search(a, el)
  a.bsearch_index{|x| x == el} || -1
end
a.binary_search(&x).unwrap_or(-1);