正在检查NSString中的平衡分隔符

Question

我的输入（NSString）可以是("text")、{("text")}或(“text”){{“text”}}。在所有这些情况下，我必须确保开头分隔符（{）有自己的结束分隔符（}）。

例如，{{“text”})应标记为错误。

我正在尝试NSScanner来实现这一点，还尝试反转字符串并比较每个字符以寻找相反的字符，但遇到了一些麻烦。

什么是最好的方法？

这是我尝试的最新方法：

NSMutableString *reversedString = [NSMutableString string];
NSInteger charIndex = [_expressionTextField.text length];
while (charIndex > 0) {
    charIndex--;
    NSRange subStrRange = NSMakeRange(charIndex, 1);
    [reversedString appendString:[_expressionTextField.text substringWithRange:subStrRange]];
}
NSString *mystring = _expressionTextField.text;
NSLog(@"%@", reversedString);
for (int i = 0; i < reversedString.length; i++) {
    if ([mystring characterAtIndex:i] == [reversedString characterAtIndex:(reversedString.length -i)]) {
        NSLog(@"Closed the bracket");
    }
}

Answer 1

我用NSScanner破解了它。对于很长的字符串，我认为这会比vikingsegundo的快一点，因为我只是一次直接穿过一个字符。没有搜索或生成子字符串。对于大多数目的来说，这可能不会有什么不同。

/// Takes a string and a dictionary of delimiter pairs in which the keys are the
/// opening characters of the pairs and the values the closers. Returns YES if the 
/// delimiters in the string are balanced, otherwise NO. Ignores any characters
/// not present in the dictionary.
///
/// Note: Does not support multi-character delimiters.
BOOL stringHasBalancedDelimiters(NSString * s, NSDictionary * delimiterPairs)
{
    NSMutableArray * delimiterStack = [NSMutableArray array];
    NSString * openers = [[delimiterPairs allKeys] componentsJoinedByString:@""];
    NSString * closers = [[delimiterPairs allValues] componentsJoinedByString:@""];
    NSCharacterSet * openerSet = [NSCharacterSet characterSetWithCharactersInString:openers];
    NSCharacterSet * closerSet = [NSCharacterSet characterSetWithCharactersInString:closers];
    NSMutableCharacterSet * delimiterSet = [openerSet mutableCopy];
    [delimiterSet formUnionWithCharacterSet:closerSet];
    NSScanner * scanner = [NSScanner scannerWithString:s];
    while( ![scanner isAtEnd] ){
        // Move up to the next delimiter of either kind
        [scanner scanUpToCharactersFromSet:delimiterSet intoString:nil];
        NSString * delimiter;
        // Could be a closer.
        if( [scanner WSSScanSingleCharacterFromSet:closerSet intoString:&delimiter] ){
            // Got a paired closer; pop the opener off the stack and continue.
            NSString * expected = [delimiterStack lastObject];
            if( [expected isEqualToString:delimiter] ){
                [delimiterStack removeLastObject];
                continue;
            }
            // Not the right closer, but if the members of the pair are
            // identical, treat as an opener.
            else if( [delimiterPairs[delimiter] isEqualToString:delimiter] ){
                [delimiterStack addObject:delimiterPairs[delimiter]];
                continue;
            }
            // Otherwise this is a failure.
            else {
                return NO;
            }
        }
        // Otherwise it's an opener (or nothing, thus the if).
        if( [scanner WSSScanSingleCharacterFromSet:openerSet intoString:&delimiter] ){
            [delimiterStack addObject:delimiterPairs[delimiter]];
        }
    }
    // Haven't failed and nothing left to pair? Success.
    return [delimiterStack count] == 0;
}

我在NSScanner中添加了一个方法，使我的生活更轻松。这样，我们就不必扫描一堆字符（因为分隔符可以相邻），然后将它们拆分为单独的NSStrings。

@interface NSScanner (WSSSingleCharacter)
- (BOOL)WSSScanSingleCharacterFromSet:(NSCharacterSet *)charSet intoString:(NSString * __autoreleasing *)string;
@end
@implementation NSScanner (WSSSingleCharacter)
- (BOOL)WSSScanSingleCharacterFromSet:(NSCharacterSet *)charSet intoString:(NSString *__autoreleasing *)string
{
    if( [self isAtEnd] ) return NO;
    NSUInteger loc = [self scanLocation];
    unichar character = [[self string] characterAtIndex:loc];
    if( [charSet characterIsMember:character] ){
        if( string ){
            *string = [NSString stringWithCharacters:&character length:1];
        }
        [self setScanLocation:loc+1];
        return YES;
    }
    else {
        return NO;
    }
}
@end

一些测试：

NSDictionary * delimiterPairs = @{@"{" : @"}",
                                  @"[" : @"]",
                                  @""" : @""",
                                  @"'" : @"'",
                                  @"(" : @")"};
// Balanced simple nesting
NSString * s = @"{("text")}";
// Balanced complex nesting
NSString * t = @"{({}'(text)[""]')text}";
// Balanced symmetrical delimiters at beginning and end of string, as
// well as after both an opener and closer from a different pair
NSString * u = @"""("text""")""";
// Out of order
NSString * v = @"{("text)"}";
// Unpaired at the beginning
NSString * w = @""{text}";
// Unpaired at the end
NSString * x = @""'text'"(";
// Unpaired in the middle
NSString * y = @"[(text)']";
for( NSString * string in @[s, t, u, v, w, x, y] ){
    BOOL paired = stringHasBalancedDelimiters(string, delimiterPairs);
    NSLog(@"%d", paired);
}

Answer 2

您必须跟踪最新的分隔符及其出现的位置。

你可以给我们一个堆栈：通过上面找到的每个开头分隔符。当你找到正确的结尾分隔符时，删除最后一个。

#import <Foundation/Foundation.h>
int main(int argc, const char * argv[])
{
    @autoreleasepool {
        NSMutableArray *stack = [NSMutableArray array];
        NSString *text = @"(“text”){{“text”}}}";
        NSArray *delimiterPairs = @[@[@"(", @")"],@[@"{", @"}"]];
        NSMutableString *openingDelimiters = [@"" mutableCopy];
        NSMutableString *closingDelimiters = [@"" mutableCopy];
        [delimiterPairs enumerateObjectsUsingBlock:^(NSArray *pair, NSUInteger idx, BOOL *stop) {
            [openingDelimiters appendString:pair[0]];
            [closingDelimiters appendString:pair[1]];
        }];
        NSScanner *scanner = [NSScanner scannerWithString:text];
        __block BOOL unbalanced = NO;
        while (![scanner isAtEnd] && !unbalanced) {
            [scanner scanUpToCharactersFromSet:[NSCharacterSet characterSetWithCharactersInString:[openingDelimiters stringByAppendingString:closingDelimiters]]
                                    intoString:NULL];
            NSString *currentDelimiter = [text substringWithRange:NSMakeRange([scanner scanLocation], 1)];
            if ([openingDelimiters rangeOfString:currentDelimiter].location != NSNotFound) {
                [stack addObject:currentDelimiter];
            } else {
                [delimiterPairs enumerateObjectsUsingBlock:^(NSArray *pair, NSUInteger idx, BOOL *stop) {
                    if([currentDelimiter isEqualToString:pair[1]]){
                        if([stack count] == 0) {
                            unbalanced = YES;
                        } else if ([[stack lastObject] isEqualToString:pair[0]]) {
                            [stack removeLastObject];
                        }
                        *stop = YES;
                    }
                }];
            }
            scanner.scanLocation +=1;
        }
        if ([stack count])
            unbalanced = YES;            
    }
    return 0;
}

如果分隔符不匹配，则布尔不平衡将为YES；