objective c - Invertir texto NSString

objective-c cocoa

Question

He estado buscando en Google sobre cómo hacer esto, pero ¿cómo iba a revertir un NSString? Ej .: hola se convertiría en: ih

Estoy buscando la manera más fácil de hacer esto.

¡Gracias!

@Vince hice este método:

- (IBAction)doneKeyboard {

// first retrieve the text of textField1
NSString *myString = field1.text;
NSMutableString *reversedString = [NSMutableString string];
NSUInteger charIndex = 0;
while(myString && charIndex < [myString length]) {
    NSRange subStrRange = NSMakeRange(charIndex, 1);
    [reversedString appendString:[myString substringWithRange:subStrRange]];
    charIndex++;
}
// reversedString is reversed, or empty if myString was nil
field2.text = reversedString;
}

Conecté ese método a didendonexit de textfield1. Cuando hago clic en el botón hecho, no se invierte el texto, UILabel solo muestra el texto de UITextField que ingresé. ¿Qué está mal?

Answer 1

¿Sería más rápido si solo iteraras más de la mitad de la cadena intercambiando los caracteres en cada extremo? Entonces, para una cadena de 5 caracteres, intercambias los caracteres 1 + 5, luego 2 + 4 y 3 no necesitan intercambiarse con nada.

NSMutableString *reversed = [original mutableCopyWithZone:NULL];
NSUInteger i, length;

length = [reversed length];

for (i = 0; i < length / 2; i++) {
    // Store the first character as we''re going to replace with the character at the end
    // in the example, it would store ''h'' 
    unichar startChar = [reversed characterAtIndex:i];

    // Only make the end range once
    NSRange endRange = NSMakeRange(length - i, 1);

    // Replace the first character (''h'') with the last character (''i'')
    // so reversed now contains "ii"
    [reversed replaceCharactersInRange:NSMakeRange(i, 1) 
                            withString:[reversed subStringWithRange:endRange];

    // Replace the last character (''i'') with the stored first character (''h)
    // so reversed now contains "ih"
    [reversed replaceCharactersInRange:endRange
                            withString:[NSString stringWithFormat:@"%c", startChar]];
}

editar ----

Después de haber hecho algunas pruebas, la respuesta es No, es aproximadamente 6 veces más lenta que la versión que recorre todo. Lo que nos ralentiza es crear las NSStrings temporales para el método replaceCharactersInRange: withString. Aquí hay un método que crea solo un NSString manipulando los datos del personaje directamente y parece mucho más rápido en pruebas simples.

NSUInteger length = [string length];
unichar *data = malloc(sizeof (unichar) * length);
int i;

for (i = 0; i < length / 2; i++) {
    unichar startChar = [string characterAtIndex:i];
    unichar endChar = [string  characterAtIndex:(length - 1) - i];

    data[i] = endChar;
    data[(length - 1) - i] = startChar;
}

NSString *reversed = [NSString stringWithCharacters:data length:length];
free(data);

Answer 2

Agregue una categoría a NSString para poder invocar inversamente en cualquier NSString en el futuro de esta manera:

#import "NSString+Reverse.h"

@implementation NSString (Reverse)
-(NSString*)reverse {
  char* cstring = (char*)[self UTF8String];
  int length = [self length]-1;

  int i=0;

  while (i<=length) {
    unichar tmp = cstring[i];
    cstring[i] = cstring[length];
    cstring[length] = tmp;
    i++;
    length--;
  }

  return [NSString stringWithCString:cstring encoding:NSUTF8StringEncoding];

}
@end

Answer 3

Aquí hay una colección de categorías en Objective-C que revertirán tanto NSStrings como NSAttributedStrings (conservando los atributos de los caracteres): TextFlipKit

Por ejemplo:

NSString *example = @"Example Text";

NSString *reversed = example.tfk_reversed;

NSLog(@"Reversed: %@", reversed);

//prints ''Reversed: txeT elpmaxE''

Answer 4

Escribí una categoría sobre esa: D

//NSString+Reversed.h # import

//
//  NSString+Reversed.h
//  HTMLPageFormatter
//  Created by beit46 on 21.06.13.
//  

@interface NSString (Reversed)
- (NSString *)reversedString;
@end

//NSString+Reversed.m

//
//  NSString+Reversed.m
//  HTMLPageFormatter
//  Created by beit46 on 21.06.13.
#import "NSString+Reversed.h"

@implementation NSString (Reversed)
- (NSString *)reversedString {
    NSMutableString *reversedString = [NSMutableString stringWithCapacity:[self length]];

    [self enumerateSubstringsInRange:NSMakeRange(0,[self length])
                                 options:(NSStringEnumerationReverse | NSStringEnumerationByComposedCharacterSequences)
                              usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) {
                                  [reversedString appendString:substring];
                              }];
    return [reversedString copy];
}
@end

Answer 5

Escribe un bucle simple para hacer eso:

// myString is "hi"
NSMutableString *reversedString = [NSMutableString string];
NSInteger charIndex = [myString length];
while (charIndex > 0) {
    charIndex--;
    NSRange subStrRange = NSMakeRange(charIndex, 1);
    [reversedString appendString:[myString substringWithRange:subStrRange]];
}
NSLog(@"%@", reversedString); // outputs "ih"

En tu caso:

// first retrieve the text of textField1
NSString *myString = textField1.text;
NSMutableString *reversedString = [NSMutableString string];
NSInteger charIndex = [myString length];
while (myString && charIndex > 0) {
    charIndex--;
    NSRange subStrRange = NSMakeRange(charIndex, 1);
    [reversedString appendString:[myString substringWithRange:subStrRange]];
}
// reversedString is reversed, or empty if myString was nil
textField2.text = reversedString;

Answer 6

Invierta la cadena usando recursión:

@implementation NSString (Reversed)

+ (NSString *)reversedStringFromString:(NSString *)string
{
    NSUInteger count = [string length];

    if (count <= 1) { // Base Case
        return string;
    } else {
        NSString *lastLetter = [string substringWithRange:NSMakeRange(count - 1, 1)];
        NSString *butLastLetter = [string substringToIndex:count - 1];
        return [lastLetter stringByAppendingString:[self reversedStringFromString:butLastLetter]];
    }
}

@end

Answer 7

La respuesta de jano es correcta. Desafortunadamente, crea una gran cantidad de objetos temporales innecesarios. Aquí hay una implementación mucho más rápida (más complicada) que básicamente hace lo mismo, pero usa los búferes memcpy y unichar para mantener las asignaciones de memoria al mínimo.

- (NSString *)reversedString
{
    NSUInteger length = [self length];
    if (length < 2) {
        return self;
    }

    unichar *characters = calloc(length, sizeof(unichar));
    unichar *reversedCharacters = calloc(length, sizeof(unichar));
    if (!characters || !reversedCharacters) {
        free(characters);
        free(reversedCharacters);
        return nil;
    }

    [self getCharacters:characters range:NSMakeRange(0, length)];

    NSUInteger i = length - 1;
    NSUInteger copiedCharacterCount = 0;

    // Starting from the end of self, copy each composed character sequence into reversedCharacters
    while (copiedCharacterCount < length) {
        NSRange characterRange = [self rangeOfComposedCharacterSequenceAtIndex:i];
        memcpy(reversedCharacters + copiedCharacterCount, characters + characterRange.location, characterRange.length * sizeof(unichar));
        i = characterRange.location - 1;
        copiedCharacterCount += characterRange.length;
    }

    free(characters);

    NSString *reversedString = [[NSString alloc] initWithCharactersNoCopy:reversedCharacters length:length freeWhenDone:YES];
    if (!reversedString) {
        free(reversedCharacters);
    }

    return reversedString;
}

Probé esto en 100,000 cadenas de Unicode multibyte al azar con longitudes entre 1 y 128. Esta versión es aproximadamente 4-5 veces más rápida que la de jano.

Enumerate substrings: 2.890528
MemCopy: 0.671090
Enumerate substrings: 2.840411
MemCopy: 0.662882

El código de prueba está en https://gist.github.com/prachigauriar/9739805 .

Actualización : Intenté esto de nuevo simplemente convirtiendo a un buffer UTF-32 y revirtiendo eso.

- (NSString *)qlc_reversedStringWithUTF32Buffer
{
    NSUInteger length = [self length];
    if (length < 2) {
        return self;
    }

    NSStringEncoding encoding = NSHostByteOrder() == NS_BigEndian ? NSUTF32BigEndianStringEncoding : NSUTF32LittleEndianStringEncoding;
    NSUInteger utf32ByteCount = [self lengthOfBytesUsingEncoding:encoding];
    uint32_t *characters = malloc(utf32ByteCount);
    if (!characters) {
        return nil;
    }

    [self getBytes:characters maxLength:utf32ByteCount usedLength:NULL encoding:encoding options:0 range:NSMakeRange(0, length) remainingRange:NULL];

    NSUInteger utf32Length = utf32ByteCount / sizeof(uint32_t);
    NSUInteger halfwayPoint = utf32Length / 2;
    for (NSUInteger i = 0; i < halfwayPoint; ++i) {
        uint32_t character = characters[utf32Length - i - 1];
        characters[utf32Length - i - 1] = characters[i];
        characters[i] = character;
    }

    return [[NSString alloc] initWithBytesNoCopy:characters length:utf32ByteCount encoding:encoding freeWhenDone:YES];
}

Esto es alrededor de 3-4 veces más rápido que la versión memcpy. La esencia antes mencionada ha sido actualizada con la última versión del código.

Enumerate substrings: 2.168705
MemCopy: 0.488320
UTF-32: 0.150822
Enumerate substrings: 2.169655
MemCopy: 0.481786
UTF-32: 0.147534
Enumerate substrings: 2.248812
MemCopy: 0.505995
UTF-32: 0.154531

Answer 8

Ninguna de las respuestas parece considerar caracteres multibyte así que aquí está mi código de muestra. Asume que solo pasas una cadena más de un caracter.

- (void)testReverseString:(NSString *)string
{
    NSMutableString *rString = [NSMutableString new];
    NSInteger extractChar = [string length] - 1;
    while (extractChar >= 0)
    {
        NSRange oneCharPos = [string rangeOfComposedCharacterSequenceAtIndex:extractChar];
        for (NSUInteger add = 0; add < oneCharPos.length; ++ add)
        {
            unichar oneChar = [string characterAtIndex:oneCharPos.location + add];
            [rString appendFormat:@"%C", oneChar];
        }
        extractChar -= oneCharPos.length;
    }

    NSLog(@"%@ becomes %@", string, encryptedString );
}

Answer 9

Pensé que lanzaría otra versión por si a alguien le interesara ... personalmente, me gusta el enfoque más limpio usando NSMutableString, pero si el rendimiento es la más alta prioridad, este es más rápido:

- (NSString *)reverseString:(NSString *)input {
    NSUInteger len = [input length];
    unichar *buffer = malloc(len * sizeof(unichar));
    if (buffer == nil) return nil; // error!
    [input getCharacters:buffer];

    // reverse string; only need to loop through first half
    for (NSUInteger stPos=0, endPos=len-1; stPos < len/2; stPos++, endPos--) {
        unichar temp = buffer[stPos];
        buffer[stPos] = buffer[endPos];
        buffer[endPos] = temp;
    }

    return [[NSString alloc] initWithCharactersNoCopy:buffer length:len freeWhenDone:YES];
}

También escribí una prueba rápida para comparar esto con el método NSMutableString más tradicional (que también incluí a continuación):

// test reversing a really large string
NSMutableString *string = [NSMutableString new];
for (int i = 0; i < 10000000; i++) {
    int digit = i % 10;
    [string appendFormat:@"%d", digit];
}
NSTimeInterval startTime = [[NSDate date] timeIntervalSince1970];
NSString *reverse = [self reverseString:string];
NSTimeInterval elapsedTime = [[NSDate date] timeIntervalSince1970] - startTime;
NSLog(@"reversed in %f secs", elapsedTime);

Los resultados fueron:

• usando el método NSMutableString (abajo) - "revertido en 3.720631 segundos"

• usando el método de buffer unichar * (arriba) - "invertido en 0.032604 segundos"

Solo como referencia, aquí está el método NSMutableString utilizado para esta comparación:

- (NSString *)reverseString:(NSString *)input {
    NSUInteger len = [input length];
    NSMutableString *result = [[NSMutableString alloc] initWithCapacity:len];
    for (int i = len - 1; i >= 0; i--) {
        [result appendFormat:@"%c", [input characterAtIndex:i]];
    }
    return result;
}

Answer 10

Rápido:

let string = "reverse"
let reversedStringCollection = string.characters.reversed()

for character in reversedStringCollection {
    reversedString.append(character)
    print(reversedString)
}

Answer 11

También podemos lograr la secuencia inversa de la siguiente manera.

NSString *originalString = @"Hello";
NSString *reverseString;
for (NSUInteger index = originalString.length; index > 0; index--) {
    char character = [originalString characterAtIndex:index];
    reverseString = [reverseString stringByAppendingString:[NSString stringWithFormat:@"%c", character]];
}

o

NSString *originalString = @"Hello";
NSString *reverseString;
for (NSUInteger index = originalString.length; index > 0; index--) {
   char *character = [originalString characterAtIndex:index];
   reverseString = [reverseString stringByAppendingString:[NSString stringWithFormat:@"%s", character]];
}

Answer 12

Tengo dos soluciones simples para ese propósito:

+(NSString*)reverseString:(NSString *)str
{
    NSMutableString* reversed = [NSMutableString stringWithCapacity:str.length];
    for (int i = (int)str.length-1; i >= 0; i--){
         [reversed appendFormat:@"%c", [str characterAtIndex:i]];
    }
    return reversed;
}

+(NSString*)reverseString2:(NSString *)str
{
    char* cstr = (char*)[str UTF8String];
    int len = (int)str.length;
    for (int i =  0; i < len/2; i++) {
        char buf = cstr[i];
        cstr[i] = cstr[len-i-1];
        cstr[len-i-1] = buf;
    }
    return [[NSString alloc] initWithBytes:cstr length:len encoding:NSUTF8StringEncoding];
}

Ahora, vamos a probarlo!

NSString* str = @"Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language";
NSLog(@"REV 1: %@", [Util reverseString:str]);
start = [NSDate date];
for (int i = 0 ; i < 1000; ++i)
    [Util reverseString:str];
end = [NSDate date];
NSLog(@"Time per 1000 repeats: %f", [end timeIntervalSinceDate:start]);

NSLog(@"REV 2: %@", [Util reverseString2:str]);
start = [NSDate date];
for (int i = 0 ; i < 1000; ++i)
    [Util reverseString2:str];
end = [NSDate date];
NSLog(@"Time per 1000 repeats: %f", [end timeIntervalSinceDate:start]);

Resultados:

ConsoleTestProject[68292:303] REV 1: egaugnal gnimmargorp C eht ot gnigassem elyts-klatllamS sdda taht egaugnal gnimmargorp detneiro-tcejbo ,esoprup-lareneg a si C-evitcejbO
ConsoleTestProject[68292:303] Time per 1000 repeats: 0.063880
ConsoleTestProject[68292:303] REV 2: egaugnal gnimmargorp C eht ot gnigassem elyts-klatllamS sdda taht egaugnal gnimmargorp detneiro-tcejbo ,esoprup-lareneg a si C-evitcejbO
ConsoleTestProject[68292:303] Time per 1000 repeats: 0.002038

Y el resultado de más caracteres fue:

ConsoleTestProject[68322:303] chars: 1982
ConsoleTestProject[68322:303] Time 1 per 1000 repeats: 1.014893
ConsoleTestProject[68322:303] Time 2 per 1000 repeats: 0.024928

El mismo texto con las funciones anteriores:

ConsoleTestProject[68366:303] Time 1 per 1000 repeats: 0.873574
ConsoleTestProject[68366:303] Time 2 per 1000 repeats: 0.019300
ConsoleTestProject[68366:303] Time 3 per 1000 repeats: 0.342735 <-Vladimir Gritsenko
ConsoleTestProject[68366:303] Time 4 per 1000 repeats: 0.584012 <- Jano

Por lo tanto, elige el rendimiento!

Answer 13

Use el método con cualquier objeto: NSString, NSNumber, etc.:

NSLog(@"%@",[self reverseObject:@12345]);
NSLog(@"%@",[self reverseObject:@"Hello World"]);

Método:

-(NSString*)reverseObject:(id)string{

string = [NSString stringWithFormat:@"%@",string];
NSMutableString *endString = [NSMutableString new];

while ([string length]!=[endString length]) {
    NSRange range = NSMakeRange([string length]-[endString length]-1, 1);
    [endString appendString: [string substringWithRange:range]];
}
return endString;}

Iniciar sesión:

2014-04-16 11:20:25.312 TEST[23733:60b] 54321
2014-04-16 11:20:25.313 TEST[23733:60b] dlroW olleH

Answer 14

Versión de bloque

NSString *myString = @"abcdefghijklmnopqrstuvwxyz";
NSMutableString *reversedString = [NSMutableString stringWithCapacity:[myString length]];

[myString enumerateSubstringsInRange:NSMakeRange(0,[myString length]) 
                             options:(NSStringEnumerationReverse | NSStringEnumerationByComposedCharacterSequences)
                          usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) {
                            [reversedString appendString:substring];
                        }];

// reversedString is now zyxwvutsrqponmlkjihgfedcba

Answer 15

Google es tu amigo :

-(NSString *) reverseString
{
  NSMutableString *reversedStr;
  int len = [self length];

  // Auto released string
  reversedStr = [NSMutableString stringWithCapacity:len];     

  // Probably woefully inefficient...
  while (len > 0)
    [reversedStr appendString:
         [NSString stringWithFormat:@"%C", [self characterAtIndex:--len]]];   

  return reversedStr;
}

Answer 16

Swift 2.0:

1) let str = "¡Hola, mundo!" let reversed = String (str.characters.reverse ()) print (invertido)

En breve:

String("This is a test string.".characters.reverse())

2)

let string = "This is a test string."
let characters = string.characters
let reversedCharacters = characters.reverse()
let reversedString = String(reversedCharacters)

La manera corta:

String("This is a test string.".characters.reverse())

O

let string = "This is a test string."
let array = Array(string)
let reversedArray = array.reverse()
let reversedString = String(reversedArray)
The short way :

String(Array("This is a test string.").reverse())

Probado en Play Ground:

import Cocoa

//Assigning a value to a String variable
var str = "Hello, playground"

//Create empty character Array.
var strArray:Character[] = Character[]()

//Loop through each character in the String
for character in str {
//Insert the character in the Array variable.
strArray.append(character)
}

//Create a empty string
var reversedStr:String = ""

//Read the array from backwards to get the characters
for var index = strArray.count - 1; index >= 0;--index {
//Concatenate character to String.
reversedStr += strArray[index]
}

La versión más corta:

var str = “Hello, playground”
var reverseStr = “”
for character in str {
reverseStr = character + reverseStr
}

Answer 17

-(NSString *) reverseString: (NSString *) string {
    NSMutableArray *letters = [[NSMutableArray alloc] init];
    for (int i=0; i<[string length]; i++)
        [letters addObject: [string substringWithRange: NSMakeRange(i, 1)]];
    NSArray *reversed = [[letters reverseObjectEnumerator] allObjects];
    return [reversed componentsJoinedByString: @""];
}

Answer 18

NSMutableString *result = [NSMutableString stringWithString:@""];
    for (long i = self.length - 1; i >= 0; i--) {
        [result appendFormat:@"%c", [self characterAtIndex:i]];
    }
    return (NSString *)result;

Answer 19

str=@"india is my countery";
array1=[[NSMutableArray alloc] init];
for(int i =0 ;i<[str length]; i++) {
    NSString *singleCharacter  = [NSString stringWithFormat:@"%c", [str characterAtIndex:i]];
    [array1 addObject:singleCharacter];
}


NSMutableString* theString = [NSMutableString string];

for (int i=[array1 count]-1; i>=0;i--){
    [theString appendFormat:@"%@",[array1 objectAtIndex:i]];
}

Answer 20

• NSString en char utf32 (siempre 32 bits (unsigned int))
• Marcha atrás
• char utf32 en NSString

+ (NSString *)reverseString3:(NSString *)str {
    unsigned int *cstr, buf, len = [str length], i;  
    cstr  = (unsigned int *)[str cStringUsingEncoding:NSUTF32LittleEndianStringEncoding];
    for (i=0;i < len/2;i++) buf = cstr[i], cstr[i] = cstr[len -i-1], cstr[len-i-1] = buf;
    return [[NSString alloc] initWithBytesNoCopy:cstr length:len*4 encoding:NSUTF32LittleEndianStringEncoding freeWhenDone:NO];
}

Ejemplo: Apple_is  --->  si_elppA