php数据结构与算法(PHP描述) 查找与二分法查找

<?php
/**
* 查找
*
**/
// 顺序查找
function normal_search($arrdata,$val) {
$len = count($arrdata);
if($len == 0) return -1;
for($i = 0;$i < $len; $i++ ) {
echo "find no.",$i + 1," value = ",$arrdata[$i]," is = ",$val,"? <br/>";
// 找到了
if($arrdata[$i] == $val) return $i;
}
return -1;
}

// 测试顺序查找
$arrdata = array(4,51,6,73,2,5,9,33,50,3,4,6,1,4,67);
echo normal_search($arrdata,6),"<br/>";
echo normal_search($arrdata,66),"<br/>";

// 二分法查找(针对有序的列进行查找)
function binary_search($arrdata,$val) {
$len = count($arrdata);
if($len == 0) return -1;

$start = 0;
$end = $len - 1;

while($start <= $end) {
$middle = intval(($start + $end)/2);
echo "start = ",$start," end = ",$end," middle = ",$middle,"<br/>";
if($arrdata[$middle] == $val) {
return $middle;
} elseif ($arrdata[$middle] > $val) {
$end = $middle - 1 ;
} elseif ($arrdata[$middle] < $val) {
$start = $middle + 1;
}
}
return -1;
}

// 测试一下二分法查找
$arrdata = array(1,2,3,4,5,7,8,9,11,23,56,100,104,578,1000);
echo binary_search($arrdata,578),"<br/>";
echo binary_search($arrdata,66),"<br/>";