Theoretical basis of PHP array intersection and union in algorithms and data structures

In algorithms and data structures, array intersection and union are used to find elements that appear simultaneously and at least once respectively. PHP provides array_intersect() and array_union() functions to implement these operations, which can be used in practical applications, such as finding common friends between two users.

The theoretical basis and application of PHP array intersection and union in algorithms and data structures

Theoretical basis

In algorithms and data structures, array intersection and union are two basic operations.

• Intersection: Find elements that appear in both arrays.
• Union: Find elements that appear at least once in two arrays.

PHP code implementation

PHP has built-in array_intersect() and array_union() functions to calculate arrays Intersection and union:

$array1 = [1, 2, 3, 4, 5];
$array2 = [3, 4, 5, 6, 7];

// 交集
$intersection = array_intersect($array1, $array2);

// 并集
$union = array_union($array1, $array2);

print_r($intersection); // 结果：[3, 4, 5]
print_r($union); // 结果：[1, 2, 3, 4, 5, 6, 7]

Practical case: Finding common friends of two users

Suppose we have a website where each user has a "friend" list. We want to find mutual friends between two users.

$user1Friends = [23, 45, 67, 89];
$user2Friends = [34, 45, 56, 89];

// 计算共同朋友
$commonFriends = array_intersect($user1Friends, $user2Friends);

print_r($commonFriends); // 结果：[45, 89]

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