iOS開發 字符串倒序的兩種方式，首尾互換

在面試中，經常被問到字符串倒序的面試題，下面提供兩種簡單的實現：

第一種：

- (NSString*)reverseWordsInString:(NSString*)oldStr{

    NSMutableString *newStr = [[NSMutableString alloc] initWithCapacity:oldStr.length];

    for (int i = (int)oldStr.length - 1; i >= 0; i --) {

        unichar character = [oldStr characterAtIndex:i];

        [newStr appendFormat:@"%c",character];

    }

    return newStr;

}

第二種：

- (NSString*)reverseWordsInString:(NSString*)oldStr

{

    NSMutableString *newStr = [NSMutableString stringWithCapacity:oldStr.length];

    [str enumerateSubstringsInRange:NSMakeRange(0, oldStr.length)     options:NSStringEnumerationReverse |         NSStringEnumerationByComposedCharacterSequences  usingBlock:^(NSString *substring,     NSRange substringRange, NSRange enclosingRange, BOOL *stop){

    [newStr appendString:substring];

    }];

    return newStr;

}