检查括号有效性

Boolean (^isValid)(NSString *string) = ^Boolean(NSString *string) {
            NSMutableArray *stack = [NSMutableArray new];
            NSDictionary *dic = @{@"(":@")",@"[":@"]",@"{":@"}"};
            
            
            for (int i = 0; i < string.length; i++) {
                NSString *tmp = [string substringWithRange:NSMakeRange(i, 1)];
                if (dic[tmp]) {
                    [stack addObject:tmp];
                    continue;
                }
                
                for (NSString *key in dic.allKeys) {
                    NSString *value = dic[key];
                    if ([value isEqualToString:tmp]) {
                        if (![stack.lastObject isEqualToString:key]) {
                            return false;
                        }
                        
                        [stack removeLastObject];
                        break;
                    }
                }
            }
            return ![stack count];
        };

• true: isValid(@"{[]}");
• true: isValid(@"{[([{({})}])]}");
• false: isValid(@"{]}");
• true: isValid(@"{(dad)[3223]}");