How to find duplicate letter in array in C - arrays

Question

I am making a program which requires the user to input an argument (argv[1]) where the argument is every letter of the alphabet rearranged however the user likes it. Examples of valid input is "YTNSHKVEFXRBAUQZCLWDMIPGJO" and "JTREKYAVOGDXPSNCUIZLFBMWHQ". Examples of invalid input would then be "VCHPRZGJVTLSKFBDQWAXEUYMOI" and "ABCDEFGHIJKLMNOPQRSTUYYYYY" since there are duplicates of 'V' and 'Y' in the respective examples.
What I know so far is, that you can loop through the whole argument like the following
for (int j = 0, n = strlen(argv[1]); j < n; j++)
{
//Place something in here...
}
However, I do not quite know if this would be the right way to go when looking for duplicates? Furthermore, I want the answer to be as simple as possible, right know time and cpu usage is not a priority, so "the best" algorithm is not necessarily the one I am looking for.

Answer 1

Try it.
#include <stdio.h>
#include <stddef.h>
int main()
{
char * input = "ABCC";
/*
*For any character, its value must be locate in 0 ~ 255, so we just
*need to check counter of corresponding index whether greater than zero.
*/
size_t ascii[256] = {0, };
char * cursor = input;
char c = '\0';
while((c=*cursor++))
{
if(ascii[c] == 0)
++ascii[c];
else
{
printf("Find %c has existed.\n", c);
break;
}
}
return 0;
}

Answer 2

assuming that all your letters are capital letters you can use a hash table to make this algorithm work in O(n) time complexity.
#include<stdio.h>
#include<string.h>
int main(int argc, char** argv){
int arr[50]={};
for (int j = 0, n = strlen(argv[1]); j < n; j++)
{
arr[argv[1][j]-'A']++;
}
printf("duplicate letters: ");
for(int i=0;i<'Z'-'A'+1;i++){
if(arr[i]>=2)printf("%c ",i+'A');
}
}
here we make an array arr initialized to zeros. this array will keep count of the occurrences of every letter.
and then we look for letters that appeared 2 or more times those are the duplicated letters.
Also using that same array you can check if all the letters occured at least once to check if it is a permutation

Answer 3

I don't know if this is the type of code that you are looking for, but here's what I did. It looks for the duplicates in the given set of strings.
#include <stdio.h>
#include <stdlib.h>
#define max 50
int main() {
char stringArg[max];
int dupliCount = 0;
printf("Enter A string: ");
scanf("%s",stringArg);
system("cls");
int length = strlen(stringArg);
for(int i=0; i<length; i++){
for(int j=i+1; j<length; j++){
if(stringArg[i] == stringArg[j]){
dupliCount +=1;
}
}
}
if(dupliCount > 0)
printf("Invalid Input");
printf("Valid Input");
}

Answer 4

This code snippet is used to count the duplicate letters in the array.
If you want to remove the letters, Also this code snippet is helpful .Set null when the same characters are in the same letter.
#include <stdio.h>
#include <stdlib.h>
int main()
{
int count=0;
int array[]={'e','d','w','f','b','e'};
for(int i=0;i<array.Lenth;i++)
{
for(int j=1;j<array.Length;j++)
{
if(array[i]==array[j])
{
count++;
}
}
}
printf("The dublicate letter count is : %d",count);
}