1.反转函数的实现

array_reverse(array,preserve)

<?php
function array_rev($arr){
  $n = count($arr);
  $left = 0;
  $right = $n-1;
  while($left < $right){
      $tmp = $arr[$left];
      $arr[$left] = $arr[$right];
      $left++;
      $arr[$right] = $tmp;
      $right--;
  }
  return $arr;
}
$a = array(1, 2, 3, 4);
$result = array_rev($a);
print_r($result);

Array ( [0] => 4 [1] => 3 [2] => 2 [3] => 1 )

？？？？？(解决)所以数组都可以翻转，这里仅仅是从0开始的索引数组可以执行。

<?php
function array_rev($arr){
  $kArr = array_keys($arr);
  $vArr = array_values($arr);
  $n = count($arr);
  $left = 0;
  $right = $n - 1;
  while($left < $right){
    $vtemp = $vArr[$left];
    $ktemp = $kArr[$left];
    $vArr[$left] = $vArr[$right];
    $kArr[$left] = $kArr[$right];
    $left++;
    $vArr[$right] = $vtemp;
    $kArr[$right] = $ktemp;
    $right--;
  }
  return array_combine($kArr, $vArr);
}
$arr = array('a'=>'1', 3, 4, 'c'=>'22dsad');
print_r(array_rev($arr));

Array ( [c] => 22dsad [1] => 4 [0] => 3 [a] => 1 )

2.两个有序int数组是否有相同元素的最优算法

<?php
function array_common($arr1, $arr2){
  $i = 0;
  $j = 0;
  $arr_common = [];
  $n1 = count($arr1);
  $n2 = count($arr2);
  while($i < $n1 && $j < $n2){
    if($arr1[$i] < $arr2[$j]){
      $i++;
    }elseif($arr1[$i] > $arr2[$j]){
      $j++;
    }else{
      $arr_common[] = $arr1[$i];
      $i++;
      $j++;
    }
  }
  return $arr_common;
}
$arr1 = array(1, 2, 3, 4);
$arr2 = array(3, 4, 5);
var_dump(array_common($arr1, $arr2));

array (size=2)
0 => int 3
1 => int 4

3.两个数组否有相同元素的最优算法

<?php
function array_common($arr1, $arr2){
  $merge_array = array_merge($arr1, $arr2);
  // var_dump($merge_array);
  $str = implode('',$merge_array);
  $new_arr = str_split($str);
  // var_dump($new_arr);
  $result = array_count_values($new_arr);

  $arr_common = array();
  foreach ($result as $k => $v) {
    if($v >= 2){
      $arr_common[] = $k;
    }
  }
  return $arr_common;
}
$arr1 = array('a', 2, 3);
$arr2 = array(3, 4, 5, 'a');
var_dump(array_common($arr1, $arr2));

array (size=2)
0 => string 'a' (length=1)
1 => int 3

4.array_intersect(array1,array2,array3...);

比较两个数组的键值，并返回交集

<?php
$a1=array("a"=>"red","b"=>"green","c"=>"blue","d"=>"yellow");
$a2=array("e"=>"red","f"=>"green","g"=>"blue");

$result=array_intersect($a1,$a2);
print_r($result);
?>

Array ( [a] => red [b] => green [c] => blue )

5.PHP去除数组中重复数据的两个例子：一

<?php
$input = array("a" => "green","", "red","b" => "green", "","blue", "red","c" => "witer","hello","witer");
// $result = array_unique($input); //去除重复元素
$result = a_array_unique($input);   //只留下单一元素
foreach($result as $a1)
{
echo $a1 . "<br />";
}

function a_array_unique($array)//写的比较好（写方法）
{
  $out = array();
  foreach($array as $k => $v){
    if(!in_array($v,$out)){
        $out[$k] = $v;
    }
  }
  return $out;
}

green

red
blue
witer
hello

6.PHP去除数组中重复数据的两个例子：二

7.array_keys(array,value,strict)

返回包含数组中所有键名的一个新数组

<?php
$a=array("Volvo"=>"XC90","BMW"=>"X5","Toyota"=>"Highlander");
print_r(array_keys($a));
?>

Array ( [0] => Volvo [1] => BMW [2] => Toyota )

8.join(separator,array)

把数组元素组合为一个字符串

<?php
$arr = array('Hello','World!','I','love','Shanghai!');
echo join(" ",$arr);
?>

Hello World! I love Shanghai!

9.数组指针

<?php
$people = array("Bill", "Steve", "Mark", "David");

echo current($people) . "<br>"; // 当前元素是 Bill
echo next($people) . "<br>"; // Bill 的下一个元素是 Steve
echo current($people) . "<br>"; // 现在当前元素是 Steve
echo prev($people) . "<br>"; // Steve 的上一个元素是 Bill
echo end($people) . "<br>"; // 最后一个元素是 David
echo prev($people) . "<br>"; // David 之前的元素是 Mark
echo current($people) . "<br>"; // 目前的当前元素是 Mark
echo reset($people) . "<br>"; // 把内部指针移动到数组的首个元素，即 Bill
echo next($people) . "<br>"; // Bill 的下一个元素是 Steve

print_r (each($people)); // 返回当前元素的键名和键值（目前是 Steve），并向前移动内部指针
?>

Array ( [1] => Steve [value] => Steve [0] => 1 [key] => 1 )