如何找到字符串中的第一个非重复字符? [英] How can I find the first non-repeating character in a string?

问题描述

我需要编写一个函数，该函数返回字符串中的第一个非重复字符(不区分大小写).例如，对于字符串"Thanks for visiting"，它应返回"h".

I need to write a function that returns the first non-repeating character in a string (case-insensitively). For example, for the string "Thanks for visiting" it should return "h".

推荐答案

您可以在字符串中传递字符，并将每个字符的计数(以不区分大小写的方式)存储在哈希中.然后再次通过并返回计数为1的第一个字符:

You could make a pass over the characters in the string and store counts for each character (in a case-insensitive manner) in a hash. Then make another pass and return the first character with the count of 1:

sub get_char {
    my ($string) = @_;
    my @chars = split //, $string;
    my %chars;
    ++$chars{ lc() } for @chars;
    $chars{ lc() } == 1 && return $_ for @chars;
}

显然，这种方法需要花费O(n)的时间和O(n)的额外空间.

Apparently, this approach takes O(n) time and O(n) extra space.

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