[php] 数据结构&算法(PHP描述) 查找&&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/>";