java - php有什么数据结构可以实现双向索引查询？

<code>$test = [
    'a'=>'a1',
    'b'=>'a1',
    'c'=>'c1',
]
</code>

<code>$test = [
    'a'=>'a1',
    'b'=>'a1',
    'c'=>'c1',
]
</code>

<code class="php"><?php
$array = array(0 => 'blue', 1 => 'red', 2 => 'green', 3 => 'red');
$key = array_search('green', $array); // $key = 2;
$key = array_search('red', $array);   // $key = 1;
?> </code>

<code><?php
$a=array("a"=>"Dog","b"=>"Dog","c"=>5,"d"=>"5");
print_r(array_keys($a,"Dog"));
//Array ( [0] => a [1] => b )
 ?>
 </code>

<code class="php">$test = [
    'a' => 'a1',
    'b' => 'b1',
    'c' => 'c1',
    'd' => 'd1',
    'e' => 'd1'
];

//去除重复的值
$test = array_unique($test);</code>

<code class="php">$test = [
    'a' => 'a1',
    'b' => 'b1',
    'c' => 'c1',
    'd' => 'd1',
    'e' => 'd1'
];

$test = array_unique($test);

$wocao = array_flip($test);
var_dump($wocao);
</code>

<code>array(4) {
  ["a1"]=> string(1) "a"
  ["b1"]=> string(1) "b"
  ["c1"]=> string(1) "c"
  ["d1"]=> string(1) "d"
}</code>

<code>$test = [
    'a' => 'a1',
    'b' => 'b1',
    'c' => 'c1',
    'd' => 'd1',
    'e' => 'd1'
];

$test = array_unique($test);

$wocao = array_flip($test);

$test['a'];   //a1
$wocao['a1']; //a</code>

<code>$arr = array('a' => 'a1', 'b' => 'a1', 'c' => 'c1');
var_export( array_keys($arr, 'a1') ); //输出键名 a 和 b</code>