从NSString中删除所有重复的字符 [英] Remove all duplicate characters from NSString

问题描述

如何使用标准方法（无需通过源字符串进行手动迭代）？

How to do this using standard methods (without manual iteration through source string)?

PS：最后我想获取源字符串的排序字符。我试图使用 NSCharacterSet ，但找不到一种方法来将字符集转换为字符串（不迭代集合）。

PS: At final I want to get sorted characters of source string. I tried to use NSCharacterSet, but can't find a method to convert character set to string (without iterating the set).

推荐答案

没有内置的方法，但是很容易迭代字符串的字符并构建一个新的字符串，而不会有重复：

There is no built-in method for this, but it's pretty easy to iterate over the characters of the string and build a new string without duplicates:

NSString *input = @"addbcddaa";
NSMutableSet *seenCharacters = [NSMutableSet set];
NSMutableString *result = [NSMutableString string];
[input enumerateSubstringsInRange:NSMakeRange(0, input.length) options:NSStringEnumerationByComposedCharacterSequences usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) {
    if (![seenCharacters containsObject:substring]) {
        [seenCharacters addObject:substring];
        [result appendString:substring];
    }
}];
NSLog(@"String with duplicate characters removed: %@", result);
NSLog(@"Sorted characters in input: %@", [seenCharacters.allObjects sortedArrayUsingSelector:@selector(compare:)]);

这将导致字符串adbc （重复删除）和排序的唯一字符数组 [a，b，c，d] 。

This results in the string "adbc" (duplicates removed) and the sorted array of unique characters ["a", "b", "c", "d"].

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