20、Perl编程：递归、记忆化与正则表达式详解

Perl编程：递归、记忆化与正则表达式详解

1. 递归与二分查找

递归是一种强大的编程技术，它允许函数调用自身来解决问题。在搜索有序数组时，二分查找是一种高效的算法，它利用递归将问题不断分解为更小的子问题。

my @numbers = map { $_ * 3 } ( 0 .. 1000 );
sub search {
    my ( $numbers, $target ) = @_;
    return _binary_search( $numbers, $target, 0, $#$numbers );
}
sub _binary_search {
    my ( $numbers, $target, $low, $high ) = @_;
    return if $high < $low;
    # divide array in two
    my $middle = int( ( $low + $high ) / 2 );
    if ( $numbers->[$middle] > $target ) {
        # search the lower half
        return _binary_search( $numbers, $target, $low, $middle - 1 );
    }
    elsif ( $numbers->[$middle] < $target ) {
        # search the upper half
        return _binary_search( $numbers, $target, $middle