Find the highest repeated character in string and the count of the repeated character

Question

I need to get the highest repeated character in string and the count of the repeated character. For that i stored the each character of the string in the array and using the for loops i got each character and the count. is there any other delegate methods to find it to reduce the code?

for example

NSRange theRange = {0, 1}; //{location, length}
NSMutableArray * array = [NSMutableArray array];
for ( NSInteger i = 0; i < [myFormattedString length]; i++) {
    theRange.location = i;
    [array addObject:[myFormattedString substringWithRange:theRange]];
}
int countForChar = 0;
for (int i=0; i<[array count]; i++) {
    NSString *firstCharacter = [array objectAtIndex:i];
    for (int j=1; j< [array count]; j++) {
        if ([firstCharacter isEqualToString:[array objectAtIndex:j]]) {
            countForChar = countForChar + 1;
        }
    }
    NSLog(@"The Charcter is %@ The count is %d", firstCharacter, countForChar);
    countForChar = 0;
}

Thanks in advance...

Answer 1

Here is my code might be not good enough but I think its the fastest

NSString *myFormattedString = @"oksdflajdsfd";

    NSMutableDictionary *lettersCount = [[NSMutableDictionary alloc] init];
    for (NSInteger i = 0; i < [myFormattedString length]; i++) {
        unichar charAtIndex = [myFormattedString characterAtIndex:i];
        NSNumber *countForThisChar = [lettersCount objectForKey:[NSString stringWithFormat:@"%c",charAtIndex]];
        int count = 1;
        if(countForThisChar) {
            count = [countForThisChar integerValue] + 1;
            [lettersCount setObject:@(count) forKey:[NSString stringWithFormat:@"%c",charAtIndex]];
        } else {
            // not added yet, add it with 1 count
            [lettersCount setObject:@(count) forKey:[NSString stringWithFormat:@"%c",charAtIndex]];
        }
    }

    // for now the work is O(n)

    // ignoring the work of this cycle or consider it as O(1)
    NSString *mostFrequentChar = nil;
    NSInteger maxCount = 0;
    for(NSString *oneChar in lettersCount.keyEnumerator) {
        NSNumber *count = [lettersCount objectForKey:oneChar];
        if([count integerValue] > maxCount) {
            mostFrequentChar = oneChar;
            maxCount = [count integerValue];
        }
    }

    NSLog(@"the char %@ met for %d times", mostFrequentChar, maxCount);

Remember the search for an object in NsDictionary is O(1) for the average case scenario.

Answer 2

Here is an example that would work correctly with any string and has linear time complexity. This uses the NSCountedSet which can be pretty useful.

NSString* string = @"This is a very wonderful string. Ølsen & ジェイソン";
NSCountedSet* characterCounts = [[NSCountedSet alloc] init];
// This ensures that we deal with all unicode code points correctly
[string enumerateSubstringsInRange:NSMakeRange(0, [string length]) options:NSStringEnumerationByComposedCharacterSequences usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) {
  [characterCounts addObject:substring];
}];
NSString* highestCountCharacterSequence = nil;
NSUInteger highestCharacterCount = 0;
for (NSString* characterSequence in characterCounts) {
  NSUInteger currentCount = [characterCounts countForObject:characterSequence];
  if (currentCount > highestCharacterCount) {
    highestCountCharacterSequence = characterSequence;
    highestCharacterCount = currentCount;
  }
}
NSLog(@"Highest Character Count is %@ with count of %lu", highestCountCharacterSequence, (unsigned long)highestCharacterCount);

Sadly, my silly example string ends up having space characters as the most repeated :)

Answer 3

Because the string may have more than a char have same most repeat count, so here is my solution:

- (NSArray *)mostCharInString:(NSString *)string count:(int *)count{
    NSMutableDictionary *dict = [NSMutableDictionary dictionary];
    int len = string.length;
    NSRange theRange = {0, 1};
    for (NSInteger i = 0; i < len; i++) {
        theRange.location = i;
        NSString *charStr = [string substringWithRange:theRange];
        int preCount = 0;
        if ([dict objectForKey:charStr]) {
            preCount = [[dict objectForKey:charStr] unsignedIntegerValue];
        }
        [dict setObject:@(preCount+1) forKey:charStr];
    }
    NSArray *sortValues = [[dict allValues] sortedArrayUsingSelector:@selector(compare:)];
    *count = [[sortValues lastObject] unsignedIntegerValue];
    return  [dict allKeysForObject:@(*count)];
}

How to use and test:

int mostRepeatCount = 0;
NSArray *mostChars = nil;
mostChars = [self mostCharInString:@"aaabbbcccc" count:&mostRepeatCount];
NSLog(@"count:%d char:%@", mostRepeatCount, mostChars);

the result is:

count:4 char:(
    c
)

try:

mostChars = [self mostCharInString:@"aaabbbccccdddd" count:&mostRepeatCount];

the result is:

count:4 char:(
    d,
    c
)

Hope to help you.

Answer 4

Every character can be presented by its int value. Make an instance of NSArray with n size (n number of unique characters string can have). Loop through string and add +1 on (int)character index in array at every cycle. When you finish the character with greatest value in array is the highest repeated character.