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* @license Apache-2.0
*
* Copyright (c) 2026 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// MODULES //
var isPositiveZero = require( '@stdlib/math/base/assert/is-positive-zero' );
var arraylike2object = require( '@stdlib/array/base/arraylike2object' );
var gfill = require( '@stdlib/blas/ext/base/gfill' ).ndarray;
var gcopy = require( '@stdlib/blas/base/gcopy' ).ndarray;
var floor = require( '@stdlib/math/base/special/floor' );
var accessors = require( './accessors.js' );
// FUNCTIONS //
/**
* Sifts a value down the heap to restore the min-heap.
*
* @private
* @param {NonNegativeInteger} root - logical root index to sift down from
* @param {PositiveInteger} size - heap size
* @param {number} value - value to sift down
* @param {NumericArray} arr - heap storage array
* @param {integer} stride - stride length
* @param {NonNegativeInteger} offset - starting offset
*/
function siftDown( root, size, value, arr, stride, offset ) {
var ridx;
var cidx;
var j;
ridx = offset + (root*stride);
j = ( root * 2 ) + 1;
while ( j < size ) {
cidx = offset + (j*stride);
// Find smaller child.
if ( j + 1 < size && arr[ offset + ((j+1)*stride) ] < arr[ cidx ] ) {
j += 1;
cidx = offset + (j*stride);
}
// Stop if element is already smaller than child.
if ( arr[ cidx ] >= value ) {
break;
}
// Move child up.
arr[ ridx ] = arr[ cidx ];
root = j;
ridx = cidx;
j = ( root * 2 ) + 1;
}
arr[ ridx ] = value;
}
// MAIN //
/**
* Computes the k maximum values of a strided array.
*
* @param {PositiveInteger} N - number of indexed elements
* @param {PositiveInteger} k - number of maximum values to return
* @param {NumericArray} x - input array
* @param {integer} strideX - stride length for `x`
* @param {NonNegativeInteger} offsetX - starting index for `x`
* @param {NumericArray} out - output array
* @param {integer} strideOut - stride length for `out`
* @param {NonNegativeInteger} offsetOut - starting index for `out`
* @returns {NumericArray} output array
*
* @example
* var x = [ 1.0, 2.0, 3.0, 4.0, 5.0 ];
* var out = [ 0.0, 0.0, 0.0 ];
*
* maxk( 5, 3, x, 1, 0, out, 1, 0 );
* // out => [ 3.0, 4.0, 5.0 ]
*/
function maxk( N, k, x, strideX, offsetX, out, strideOut, offsetOut ) {
var min;
var xo;
var yo;
var ix;
var i;
var v;
if ( N <= 0 || k <= 0 ) {
if ( k > 0 ) {
gfill( k, NaN, out, strideOut, offsetOut );
}
return out;
}
if ( N < k ) {
gcopy( N, x, strideX, offsetX, out, strideOut, offsetOut );
gfill( k - N, NaN, out, strideOut, offsetOut + (N * strideOut) );
return out;
}
if ( N === k ) {
gcopy( N, x, strideX, offsetX, out, strideOut, offsetOut );
return out;
}
xo = arraylike2object( x );
yo = arraylike2object( out );
if ( xo.accessorProtocol || yo.accessorProtocol ) {
accessors( N, k, xo, strideX, offsetX, yo, strideOut, offsetOut );
return out;
}
// Copy first k elements
gcopy( k, x, strideX, offsetX, out, strideOut, offsetOut );
// Build min-heap from first k elements
for ( i = floor(k/2)-1; i >= 0; i-- ) {
siftDown( i, k, out[ (offsetOut + i)*strideOut ], out, strideOut, offsetOut ); // eslint-disable-line max-len
}
// Cache minimum value
min = out[ offsetOut ];
// Scan remaining elements and update heap if larger than current minimum
ix = offsetX + ( k * strideX );
for ( i = k; i < N; i++ ) {
v = x[ ix ];
// If element is larger than min, replace root and sift down
if ( v > min || (v === min && isPositiveZero( v )) ) {
out[ offsetOut ] = v;
siftDown( 0, k, v, out, strideOut, offsetOut );
min = out[ offsetOut ];
}
ix += strideX;
}
return out;
}
// EXPORTS //
module.exports = maxk;
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