Removing a duplicate character from an array

Question

When reading one book with a name Cracking the coding interviewon, Gayle LaakmannI came across this question

Create an algorithm and write code to remove duplicate characters in a string without using any extra buffer. NOTE. One or two additional variables are wonderful. An additional copy of the array is missing.

and this code: -

 public static void removeDuplicates(char[] str) {
        if (str == null) {
            return;
        }
        int len = str.length;
        if (len < 2) {
            return;
        }

        int tail = 1;

        for (int i = 1; i < len; ++i) {
            int j;
            for (j = 0; j < tail; ++j) {
                if (str[i] == str[j]) {
                    break;
                }
            }
            if (j == tail) {
                str[tail] = str[i];
                ++tail;
            }
        }
        str[tail] = 0;
    }

which should remove the duplicate character from the array. I don’t seem to understand what the algorithm does, replacing the same character again and again. I thought that only I feel that the algorithm is not working, but in fact, when I run this code, it gives me the wrong outputs. Is this a serious mistake in the book or didn’t I understand the question?

Answer 1

, Algo , . : : :

str[tail] = 0;

:

    for(; tail < len;tail++){
        str[tail] = 0;
    }

---

public static void removeDuplicates(char[] str) {
        if (str == null) {
            return;
        }
        int len = str.length;
        if (len < 2) {
            return;
        }

        int tail = 1;

        for (int i = 1; i < len; ++i) {
            int j;
            for (j = 0; j < tail; ++j) {
                if (str[i] == str[j]) {
                    break;
                }
            }

            if (j == tail) {
                str[tail] = str[i];
                ++tail;
            }

        }
        for(; tail < len;tail++){
            str[tail] = 0;
        }

    }

Answer 2

Java . , , - . - 0. , , , 0, , , ( ), .

YoK 0. , , . , .

. tail.

- StringBuffer :

public static void removeDuplicates(StringBuffer str) {                        

        int len = str.length();

        // if the string as less than 2 char then it can't have duplicates.
        if (len < 2) {                         
                return;
        }

        // fist character will never be duplicate.
        // tail is the index of the next unique character.
        int tail = 1;

        // iterate from 2nd character.
        for (int i = 1; i < len; ++i) {
                int j;

                // is char at index i already in my list of uniq char?
                for (j = 0; j < tail; ++j) {
                        if (str.charAt(i) == str.charAt(j)) {
                                break;
                        }      
                }

                // if no then add it to my uniq char list.
                if (j == tail) {                       
                        str.setCharAt(tail, str.charAt(i));

                        // increment tail as we just added a new ele.
                        ++tail;
                }
        }
        // at this point the characters from index [0,tail) are unique
        // if there were any duplicates they are between [tail,input.length)
        // so truncate the length of input to tail.
        str.setLength(tail);
}

Answer 3

.

: O (n), n = length of the string

: O (1)

void removeduplicatas(char str[]){
    int i, checker = 0, bitvalue = 0, value = 0, tail = 0;
    i = 0;
    tail = 0;
    while(str[i]){
        value = str[i] - 'a';
        bitvalue = 1 << value;
        if((checker & bitvalue) == 0 ){
            str[tail++] = str[i];
            checker |= bitvalue;
        }
        i++;
    }
    str[tail] = '\0';
}

Answer 4

++ char. , , k .

#include <cstdint>
#include <iostream>

bool CheckUniqueChars(char *string, uint32_t index, uint32_t checker){

char character = string[index];

if(character=='\0'){
    return true;
}else{
    int value = character - 'a';

    if((checker&(1<<value))>0){
        return false;
    }else{
       checker |= (1<<value);
       return CheckUniqueChars(string,++index,checker);
    }
   }
}


int main(int argc, char *argv[]){

    char *string = argv[1];
    uint32_t idx=0,checker=0;

 if(CheckUniqueChars(string,idx,checker)){
        std::cout << "all characters are unique" << std::endl;
 }else{
    std::cout << "there are duplicate characters" << std::endl;
 }

 return 0;
}

Answer 5

, YoK,

for(; tail < len;tail++){
       str[tail] = 0;
}

.

public static void removeDuplicates(char[] str){
    if (str == null) {
        return;
    }
    int len = str.length;
    if (len < 2) {
        return;
    }

    int tail = 1;

    for(int i=1;i<len;++i){
        int j;
        for(j=0;j<tail;++j){
            if(str[i] == str[j]) break;
        }
        if(j==tail){
            str[tail] = str[i];
            if(i!=tail)str[i]=0;
            ++tail;
        }else{
            str[i]=0;
        }

    }
}