1 <?php
2 /**
3 sequence search
4 从第一个元素开始，依次同每个元素比较
5 */
6 function seq_search($arr,$n,$k){
7 for($i=0;$i<$n;$i++){
8 if($arr[$i]==$k){
9 break;
10 }
11 }
12 if($i<$n){
13 return $i;
14 }else{
15 return -1;
16 }
17 }
18
19 /**
20 binary search 使用了递归
21 */
22 function binary_search_recursive($arr,$low,$high,$k){
23 if($low<=$high){
24 $mid=intval(($low+$high)/2);
25 if($arr[$mid]==$k){
26 return $mid;
27 }else if($arr[$mid]<$k){
28 return binary_search($arr,$mid+1,$high,$k);
29 }else{
30 return binary_search($arr,$low,$mid-1,$k);
31 }
32 }
33 return -1;
34 }
35
36 /**
37 binary search 未使用递归
38 */
39 function binary_search($arr,$low,$high,$val){
40 $mid = floor(($low+$high)/2);
41 while($val!=$arr[$mid]&&$low<$high){
42 if($val<$arr[$mid]){
43 $high = $mid-1;
44 }
45 if($val>$arr[$mid]){
46 $low = $mid+1;
47 }
48 $mid = floor(($low+$high)/2);
49 }
50 return $val==$arr[$mid]?$mid:-1;
51 }
52
53 $arr = array(9,6,10,2,5,3,1,8);
54 echo seq_search($arr,8,2);
55 echo '<br/>';
56 echo binary_search_recursive($arr,0,7,2);
57 echo '<br/>';
58 echo binary_search($arr,0,7,2);
59
