静态查找算法

#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 == $val) {
			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;
}