Eliminate duplicates from a array of characters - c++

Question

I have to eliminate duplicates from a array of characters using pointers and a function.
I can t get it to work correctly:
void del_copy(char *p){
int n = strlen(p);
for (int i = 0; i < n; i++){ // Element that we compare
for (int j = i + 1; j < n;j++){ //We compare p + i element with the rest of the elements
if (*(p + i) == *(p + j)){ //If we find two similar, we eliminate that element by shifting
for (int k = i; k < n; k++)
*(p + k) = *(p + k + 1);
}
}
}
}

Answer 1

After you do a shift the length changes. But your n doesn't take that into account.

Answer 2

Here's a simple algorithm:
let s be the empty set (characters encountered so far)
let result be an empty string
for each character c in the input string (
if c is not in s (
include c in s and
append c to the end of result
)
)
result is the result
For the char type on an ordinary machine with 8-bit byte, you can just use a std::bitset as set s.
Another simple algorithm is to sort the string first, if there is no requirement on preserving order. Then you can just scan it and look for duplicates.

Answer 3

sample to fix
void del_copy(char *p){
char c;
for (int i = 0; c=*(p+i); i++){
char *p2, *p3;
for(p2 = p+i+1, p3 = p2; *p3; ++p3){
if(*p3 != c)
*p2++ = *p3;
}
*p2 = '\0';
}
}

Answer 4

Here's my take at the problem. It basically uses a lookup table to check if the character has been seen before but is templated. You could use any kind of value_type.
#include <algorithm>
#include <unordered_map>
template <typename Container>
Container unique_all(Container const& c) {
Container out;
::std::unordered_map<typename Container::value_type,::std::size_t> lookup;
::std::copy_if(c.begin(), c.end(),
::std::back_inserter(out),
[&](typename Container::value_type ch) {return !lookup[ch]++;});
return out;
}
You can call it like this:
unique_all(::std::string("hello dear world"))

Answer 5

I have managed to fix my own code also. Thank you everyone for support.
I had to change the if loop for a while loop and to decrement de lenght #ScottMcP-MVP.
void del_copy(char *p){
int n = strlen(p);
for (int i = 0; i < n-1; i++){ // Element that we compare
for (int j = i + 1; j < n;j++){ //We compare p + i element with the rest of the elements
while(*(p + i) == *(p + j)){ //If we find two similar, we eliminate that element by shifting
for (int k = j; k < n; k++)
*(p + k) = *(p + k + 1);
n--; //decrement n because the lenght if smaller now
}
}
}
}