Example analysis of binary search algorithm implemented in PHP

This article mainly introduces the binary search algorithm implemented in PHP. It analyzes the principles of the binary search algorithm and implementation techniques such as loops and recursions in the form of examples. Friends in need can refer to it. I hope it can help everyone.

The binary search method requires the array to be an ordered array

Assuming that our array is an increasing array, first we need to find the middle position of the array.

1. To know the middle position, you need to know the starting position and the end position, and then take the value of the middle position to compare with our value.
two. If the middle value is greater than our given value, it means that our value is before the middle position. At this time, it needs to be divided into two again. Because it is before the middle, the value we need to change is the value of the end position. At this time, the value of the end position should be We're in the middle at this point.
three. On the other hand, if the middle value is less than the value we give, it means that the given value is after the middle position. At this time, the value of the latter part needs to be divided into two again, because it is after the middle value, so the value we need to change is the starting position. value, the value of the starting position at this time should be our middle position at this time until we find the specified value.
Four. Or the intermediate value is equal to the initial starting position, or the end position (in this case, the given value is not found), let’s use code to implement it~

//循环实现
function getValue($num,$arr)
{
//查找数组的中间位置
$length=count($arr);
$start=0;
$end=$length;
$middle=floor(($start+$end)/2);
//循环判断
while($start>$end-1)
{
if($arr[middle]==$num)
{
return middle+1;
}elseif($arr[middle]<$num)
{
//如果当前要查找的值比当前数组的中间值还要打，那么意味着该值在数组的后半段
//所以起始位置变成当前的middle的值，end位置不变。
$start=$middle;
$middle=floor(($start+$end)/2);
}else{
//反之
$end=$middle;
$middle=floor(($start+$end)/2);
}}
return false;
}

//循环实现
function getValue($num,$arr)
{
//查找数组的中间位置
$length=count($arr);
$start=0;
$end=$length;
$middle=floor(($start+$end)/2);
//循环判断
while($start>$end-1)
{
if($arr[middle]==$num)
{
return middle+1;
}elseif($arr[middle]<$num)
{
//如果当前要查找的值比当前数组的中间值还要打，那么意味着该值在数组的后半段
//所以起始位置变成当前的middle的值，end位置不变。
$start=$middle;
$middle=floor(($start+$end)/2);
}else{
//反之
$end=$middle;
$middle=floor(($start+$end)/2);
}}
return false;
}

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