静态查找

顺序查找

/** * Common search. * * @param array $arr * @param mixed $item * * @return int */
public function search(array $arr, $item) {
    for ($i = 0; $i < count($arr); $i++) {
        if ($arr[$i] == $item) {
            return $i;
        }
    }

    return -1;
}

折半查找

/** * Binary search. * * @param array $arr * @param mixed $item * * @return int */
public function binSearch(array $arr, $item) {
    if (empty($arr)) {
        return -1;
    }

    $low = 0;
    $high = count($arr) - 1;

    while ($low <= $high) {
        //$mid = intval(($high + $low) / 2) 可能溢出
        $mid  = intval(($high - $low) / 2) + $low;
        $val = $arr[$mid];

        if($item == $arr) {
            return $mid;
        } elseif ($item < $val) {
            $high = $mid -1;
        } else {
            $low = $mid + 1;
        }
    }

    return -1;
}

递归折半查找

/** * Recursion binary search. * * @param array $arr * @param mixed $item * @param int $low * @param int $high * * @return int */

public function binRecSearch(array $arr, $item, $low, $high){
    if (empty($arr) || $low > $high || $low < 0) {
        return -1;
    }

    $low = 0;
    $high = count($arr) - 1;

    if ($low <= $high) {
        $mid = intval(($high - $low) / 2) + $low;
        if ($item == $arr[$mid]) {
            return $mid;
        } elseif ($item < $arr[$mid]) {
            return binRecSearch($arr, $item, $mid + 1, $high);
        } else {
            return binRecSearch($arr, $item, $low, $mid - 1);
        }
    }

    return -1;
}

插值查找（利用了元素差异性,靠近谁就向谁移动的多一些）

/** * Insert Value search * * @param array $arr * @param mixed $item * * @return int */
public function insertValSearch(array $arr, $item) {
    if (empty($arr)) {
        return -1;
    }

    $low = 0;
    $high = count($arr) - 1;

    while ($low <= $high) {
        $mid = ($high - $low) * ($item - $arr[$low]) / ($arr[$high] - $arr[$low]);

        if ($arr[$mid] == $item) {
            return $mid;
        } elseif ($arr[$mid] < $item) {
            $low = $mid + 1;
        } else {
            $high = $mid - 1;
        }
    }

    return -1;
}