PHP implements several sorting and search algorithms

Bubble sort, quick sort, and binary search are simple, but they are easy to forget if you don’t use them for a while. Here is the PHP implementation code that the editor found and shared with everyone to learn together.

Sort

Bubble sort

Every time a maximum value pops up

function bubbleSort($arr)
{
    $count = count($arr);
    if ($count == 0) return false;

    for ($i = 0; $i < $count - 1; $i++) {
        for ($k = 0; $k < $count - 1 - $i; $k++) {
            if ($arr[$k] < $arr[$k + 1]) {
                $tmp         = $arr[$k];
                $arr[$k]     = $arr[$k + 1];
                $arr[$k + 1] = $tmp;
            }
        }
    }

    return $arr;
}

Quick sort

Choose a value as a benchmark , smaller ones are placed on the left, larger ones are placed on the right, then recurse to the left and right, and finally merge

function quickSort($arr)
{
    $count = count($arr);
    if ($count <= 1) return $arr;

    $base = $arr[0];
    $left = $right = [];
    for ($i = 1; $i < $count; $i++) {
        if ($arr[$i] < $base) {
            $left[] = $arr[$i];
        } else {
            $right[] = $arr[$i];
        }
    }

    $left  = quickSort($left);
    $right = quickSort($right);

    return array_merge($left, [$base], $right);
}

Selection sort

Select a value assumed to be the smallest, and then compare in sequence, If you find it is smaller than him, swap the positions

function selectSort($arr)
{
    $count = count($arr);
    if ($count <= 1) return $arr;

    for ($i = 0; $i < $count; $i++) {
        //假设最小值位置
        $p = $i;
        //用假设的最小值$arr[$p]轮流比较，发现比他小的就互换
        for ($j = $i + 1; $j < $count; $j++) {
            if ($arr[$p] > $arr[$j]) {
                $p = $j;
            }
        }

        if ($p != $i) {
            $tmp     = $arr[$p];
            $arr[$p] = $arr[$i];
            $arr[$i] = $tmp;
        }
    }

    return $arr;
}

Search

Binary search

Binary search must be a sorted array, and each time the value in the middle position of the array is taken and Target comparison

function binarySearch(array $arr, $target)
{
    $low = 0;
    $high = count($arr) - 1;
    while ($low <= $high) {
        $middle = floor(($high + $low) / 2);
        if ( $arr[$middle] == $target ) {
            return $middle;
        } elseif ( $arr[$middle] < $target ) {
            $low = $middle + 1;
        } else {
            $high = $middle - 1;
        }
    }

    return false;
}

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