Safe Haskell	None
Language	GHC2021

AtCoder.Extra.Bisect

Contents

C++-like binary search
Generic bisection method

Description

Bisection methods and binary search functions. They partition a half-open interval \([l, r)\) into two and return either the left or the right point of the boundary.

Y Y Y Y Y N N N N N      Y: user predicate holds
--------* *---------> X  N: user predicate does not hold
        L R              L, R: left, right point of the boundary

Example

Expand

Perform index compression:

>>> import AtCoder.Extra.Bisect
>>> import Data.Vector.Algorithms.Intro qualified as VAI
>>> import Data.Vector.Unboxed qualified as VU
>>> let xs = VU.fromList ([0, 20, 10, 40, 30] :: [Int])
>>> let dict = VU.uniq $ VU.modify VAI.sort xs
>>> VU.map (lowerBound dict) xs
[0,2,1,4,3]

Since: 1.3.0.0

Synopsis

lowerBound :: (HasCallStack, Vector v a, Ord a) => v a -> a -> Int
lowerBoundIn :: (HasCallStack, Vector v a, Ord a) => Int -> Int -> v a -> a -> Int
upperBound :: (HasCallStack, Vector v a, Ord a) => v a -> a -> Int
upperBoundIn :: (HasCallStack, Vector v a, Ord a) => Int -> Int -> v a -> a -> Int
maxRight :: HasCallStack => Int -> Int -> (Int -> Bool) -> Int
maxRightM :: (HasCallStack, Monad m) => Int -> Int -> (Int -> m Bool) -> m Int
minLeft :: HasCallStack => Int -> Int -> (Int -> Bool) -> Int
minLeftM :: (HasCallStack, Monad m) => Int -> Int -> (Int -> m Bool) -> m Int

C++-like binary search

lowerBound :: (HasCallStack, Vector v a, Ord a) => v a -> a -> Int Source #

\(O(\log n)\) Returns the maximum \(r\) where \(x \lt x_i\) holds for \(i \in [0, r)\).

Y Y Y Y Y N N N N N      Y: (< x0)
--------- *---------> X  N: (>= x0)
          R              R: the right boundary point returned

Example

Expand

>>> import Data.Vector.Unboxed qualified as VU
>>> let xs = VU.fromList [1, 1, 2, 2, 4, 4]
>>> lowerBound xs 1
0

>>> lowerBound xs 2
2

>>> lowerBound xs 3
4

>>> lowerBound xs 4
4

Out of range values also return some index:

>>> lowerBound xs 0
0

>>> lowerBound xs 5
6

Since: 1.3.0.0

lowerBoundIn :: (HasCallStack, Vector v a, Ord a) => Int -> Int -> v a -> a -> Int Source #

\(O(\log n)\) Computes the lowerBound for a slice of a vector within the interval \([l, r)\).

The user predicate evaluates indices in \([l, r)\).

Constraints

(0 le l lt n)
(-1 le r le n)

Example

Expand

>>> import Data.Vector.Unboxed qualified as VU
>>> let xs = VU.fromList [10, 10, 20, 20, 40, 40]
>>> --                            *---*---*
>>> lowerBoundIn 2 5 xs 10
2

>>> lowerBoundIn 2 5 xs 20
2

>>> lowerBoundIn 2 5 xs 30
4

>>> lowerBoundIn 2 5 xs 40
4

>>> lowerBoundIn 2 5 xs 50
5

Since: 1.3.0.0

upperBound :: (HasCallStack, Vector v a, Ord a) => v a -> a -> Int Source #

\(O(\log n)\) Returns the maximum \(r\) where \(x \le x_i\) holds for \(i \in [0, r)\).

Y Y Y Y Y N N N N N      Y: (<= x0)
--------- *---------> X  N: (> x0)
          R              R: the right boundary point returned

Example

Expand

>>> import Data.Vector.Unboxed qualified as VU
>>> let xs = VU.fromList [10, 10, 20, 20, 40, 40]
>>> upperBound xs 10
2

>>> upperBound xs 20
4

>>> upperBound xs 30
4

>>> upperBound xs 39
4

Out of range values:

>>> upperBound xs 0
0

>>> upperBound xs 40
6

Since: 1.3.0.0

upperBoundIn :: (HasCallStack, Vector v a, Ord a) => Int -> Int -> v a -> a -> Int Source #

\(O(\log n)\) Computes the upperBound for a slice of a vector within the interval \([l, r)\).

The user predicate evaluates indices in \([l, r)\).
The interval \([l, r)\) is silently clamped to ensure it remains within the bounds \([0, n)\).

Example

Expand

>>> import Data.Vector.Unboxed qualified as VU
>>> let xs = VU.fromList [10, 10, 20, 20, 40, 40]
>>> --                            *---*---*
>>> upperBoundIn 2 5 xs 0
2

>>> upperBoundIn 2 5 xs 10
2

>>> upperBoundIn 2 5 xs 20
4

>>> upperBoundIn 2 5 xs 30
4

>>> upperBoundIn 2 5 xs 40
5

>>> upperBoundIn 2 5 xs 50
5

Since: 1.3.0.0

Generic bisection method

maxRight Source #

Arguments

:: HasCallStack
=> Int	\(l\)
-> Int	\(r\)
-> (Int -> Bool)	\(p\)
-> Int	Maximum \(r'\) where \(p\) holds for \([l, r')\).

\(O(\log n)\) Applies the bisection method on a half-open interval \([l, r)\) and returns the right boundary point.

Y Y Y Y Y N N N N N      Y: user predicate holds
--------- *---------> X  N: user predicate does not hold
          R              R: the right boundary point returned

Example

Expand

>>> import Data.Vector.Unboxed qualified as VU
>>> let xs = VU.fromList [10, 10, 20, 20, 30, 30]
>>> let n = VU.length xs
>>> maxRight 0 n ((<= 20) . (xs VU.!))
4

>>> maxRight 0 n ((<= 0) . (xs VU.!))
0

>>> maxRight 0 n ((<= 100) . (xs VU.!))
6

>>> maxRight 0 3 ((<= 20) . (xs VU.!))
3

Since: 1.3.0.0

maxRightM :: (HasCallStack, Monad m) => Int -> Int -> (Int -> m Bool) -> m Int Source #

\(O(\log n)\) Monadic variant of maxRight.

Since: 1.3.0.0

minLeft Source #

Arguments

:: HasCallStack
=> Int	\(l\)
-> Int	\(r\)
-> (Int -> Bool)	\(p\)
-> Int	Minimum \(l'\) where \(p\) holds for \([l', r)\)

\(O(\log n)\) Applies the bisection method on a half-open interval \([l, r)\) and returns the left boundary point.

N N N N N Y Y Y Y Y      Y: user predicate holds
--------* ----------> X  N: user predicate does not hold
        L                L: the left boundary point returned

Example

Expand

>>> import Data.Vector.Unboxed qualified as VU
>>> let xs = VU.fromList [10, 10, 20, 20, 30, 30]
>>> let n = VU.length xs
>>> minLeft 0 n ((>= 20) . (xs VU.!))
2

>>> minLeft 0 n ((>= 0) . (xs VU.!))
0

>>> minLeft 0 n ((>= 100) . (xs VU.!))
6

Since: 1.3.0.0

minLeftM :: (HasCallStack, Monad m) => Int -> Int -> (Int -> m Bool) -> m Int Source #

\(O(\log n)\) Monadic variant of maxRight.

Since: 1.3.0.0