Array of unique elements but with a condition- - objective-c

Question

I have an array of integers (NSMutable array to be exact), now i want the array to have unique elements, but there is a catch.
Condition-1. If there are 2 (even number of )elements that are similar then both the elements need to be deleted.
Condition-2. If there are 3(odd number of) elements then only 1 element shall remain in the array.
am having a bit of a problem trying to solve it.
I have tried to loop around the array with 2 temporary variables
for(int i =1;i<[tagArray count];i++){
int temp1 = [[tagArray objectAtIndex:i] intValue];
int temp2 = [[tagArray objectAtIndex:i-1] intValue];
if(temp1==temp2){
[tagArray removeObjectIdenticalTo:[tagArray objectAtIndex:i]];
[tagArray removeObjectAtIndex:i];
NSLog(#"%#",tagArray);
}
}
This code works but, when there are a lot of elements in the array the output i get is not the desired one.
P.S- the array is already being filled up randomly so i took the liberty of sorting it first.
1 more thing. please dont say abt set, i want unique elements but when i use SET see condition1 and 2. i cant perform those.

Answer 1

sort array (by ascending or descending intValue)
loop through each element (from 0 to N-1) and count number of previous equals elements (write it to equalNumbersCount).
After current number becomes not equal to previous, look at equalNumberCount and remove necessary number of elements (if this count is > 1 and even, remove all, if it's odd, remove only equalNumberCount - 1 previous elements)
Reset equalNumberCount to 0.
Something like this. Tested and seems to work fine:
NSMutableArray *arr = [#[#1, #4, #4, #2, #2, #3, #3, #3, #4, #4, #5] mutableCopy];
arr = [[arr sortedArrayWithOptions:NSSortStable usingComparator:^NSComparisonResult(id obj1, id obj2) {
return [obj1 compare:obj2];
}] mutableCopy];
uint countOfEqualElements = 1;
for (uint i = 1; i < arr.count; i++) {
NSNumber *n1 = arr[i-1];
NSNumber *n2 = arr[i];
if ( [n2 isEqualToNumber:n1]) {
countOfEqualElements++;
}
else if (countOfEqualElements > 1){
uint numToRemove = countOfEqualElements % 2 == 0 ? countOfEqualElements : countOfEqualElements - 1;
countOfEqualElements = 1;
NSRange r;
r.length = numToRemove;
r.location = i - numToRemove;
NSIndexSet * is = [NSIndexSet indexSetWithIndexesInRange:r];
[arr removeObjectsAtIndexes:is];
i -= numToRemove;
}
}

Answer 2

Though I've not tested with other elements yet, at present I think this might atleast interest you.
NSArray *localArray = #[#"1",#"23",#"2",#"3",#"4",#"5",#"5",#"9",#"1",#"11",#"10",#"1",#"23",#"3"];
NSCountedSet *countedSet= [[NSCountedSet alloc] initWithArray:localArray];
NSMutableArray *arrayToCheck = [localArray mutableCopy];
for (id obj in [localArray mutableCopy])
{
if([countedSet countForObject:obj]==2)
{
[arrayToCheck removeObject:obj inRange:NSMakeRange([[localArray mutableCopy] indexOfObject:obj], [arrayToCheck count]-[[localArray mutableCopy] indexOfObject:obj])];
}
else if ([countedSet countForObject:obj]==3)
{
[arrayToCheck removeObject:obj inRange:NSMakeRange([[localArray mutableCopy] indexOfObject:obj], [arrayToCheck count]-[[localArray mutableCopy] indexOfObject:obj])];
[arrayToCheck addObject:obj];
}
}
localArray = [NSArray arrayWithArray:arrayToCheck];
NSLog(#" array is %#",localArray);