Idiom #124 Binary search for a value in sorted array
Write the function binarySearch which returns the index of an element having the value x in the sorted array a, or -1 if no such element exists.
Programming-Idioms
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public static int binarySearch<T>(T[] a, T x)
{
var result = Array.BinarySearch<T>(a, x);
return result >= 0 ? result : -1;
}
public static int binarySearch<T>(List<T> a, T x)
{
var result = a.BinarySearch(x);
return result >= 0 ? result : -1;
}
template<typename T>
int binarySearch(const std::vector<T> &a, const T &x)
{
if(a.size() == 0) return -1;
size_t lower = 0;
size_t upper = a.size() - 1;
while(lower <= upper)
{
auto mid = lower + (upper-lower) / 2;
if(x == a[mid])
{
return (int)mid;
}
else if(x > a[mid])
{
lower = mid + 1;
}
else
{
upper = mid - 1;
}
}
return -1;
}
long binarySearch(long[] a, long x) {
long result = a.assumeSorted.lowerBound(x).length;
if (result == a.length || a[result] != x)
return -1;
return result;
}
a.binarySearch(x);
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 - First) 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.
integer function binarysearch(a,x) result(l)
integer,intent(in)::a(:)
integer,intent(in)::x
integer::r,mid
l=1
r=size(a)
do while(l<=r)
mid=l+(r-l)/2;
if(a(mid)==x)then
l=mid
return
end if
if(a(mid)<x)then
l=mid+1;
else
r=mid-1;
end if
end do
l=-1
end function binarysearch
func binarySearch(a []T, x T) int {
imin, imax := 0, len(a)-1
for imin <= imax {
imid := imin + (imax-imin) / 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
}
func binarySearch(a []T, x T) int {
if i, ok := slices.BinarySearch(a, x); ok {
return i
} else {
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;
}
int i = binarySearch(a, x);
function binarySearch(array $a, $x)
{
$imin = 0;
$imax = count($a) - 1;
while ($imin <= $imax) {
$imid = (int)floor($imin + ($imax-$imin) / 2);
if ($a[$imid] === $x) {
return $imid;
}
if ($a[$imid] < $x) {
$imin = $imid + 1;
} else {
$imax = $imid - 1;
}
}
return -1;
}
function BinarySearch(X: Integer; A: Array of Integer): Integer;
var
L, R, I, Cur, answer: Integer;
isIt :boolean;
begin
isIt := false;
answer := -1;
if Length(A) = 0 then Exit;
L := Low(A);
R := High(A);
while ((L <= R) AND (isIt = false)) do
begin
I := L + ((R - L) div 2);
Cur := A[I];
if (X = Cur) then begin
answer := i; {cur;}
isIt := true;
end;
if (X > Cur) then
L := I + 1
else
R := I - 1
end;
BinarySearch := answer;
end;
function binarySearch (x: integer; a: array of integer): integer;
var L, R, M: integer; // left, right, middle
begin
if Length(a)=0 then Exit(-1);
L := Low (a);
R := High(a);
while (L <= R) do begin
M := (L + R) div 2;
if (x = a[M]) then Exit(M); // found x in a
if (x > a[M])
then L := Succ(M)
else R := Pred(M);
end;
Exit(-1) // did not found x in a
end;
sub binary_search {
my ($x, $A, $lo, $hi) = @_;
$lo //= 0;
$hi //= @$A;
my $mid = int($lo + ($hi - $lo) / 2);
for ($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;
}
}
# Some ordered arrays to search within.
@num_array = ( 100, 200, 300, 400, 500 );
@str_array = qw( Bach Beethoven Brahms Mozart );
# Find the lowest index of a matching element.
$index = binsearch {$a <=> $b} 300, @num_array;
$index = binsearch {$a cmp $b} 'Mozart', @str_array;
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);