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RemoveDuplicates.java
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RemoveDuplicates.java
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package strings;
import java.util.LinkedHashSet;
import java.util.Set;
public class RemoveDuplicates {
/*
* Given a string that contains duplicate occurrences of characters, remove these duplicate occurrences
* Eg. Input: "abbabcddbabcdeedebc"
* Output: "abcde"
*
* Why to use LinkedHashSet instead of HashSet in this case?
* A HashSet is unordered and unsorted Set. LinkedHashSet is the ordered version of HashSet.
* The only difference between HashSet and LinkedHashSet is that LinkedHashSet maintains the insertion order.
* When we iterate through a HashSet, the order is unpredictable while it is predictable in case of LinkedHashSet.
* The reason why LinkedHashSet maintains insertion order is because the underlying data structure is a doubly-linked list.
*
* */
public static String removeDuplicates(String s) {
Set<Character> characterSet = new LinkedHashSet<>();
char[] charArr = s.toCharArray();
for(char c: charArr) {
characterSet.add(c);
}
StringBuilder sb = new StringBuilder();
for (Character character : characterSet) {
sb.append(character);
}
return sb.toString();
}
// this solution uses extra memory
// to keep all characters present in string.
// Null terminating strings are not used in Java.
// For this question, assume that you are passed a
// null terminated string (array of characters).
/*
* Runtime Complexity - Linear O(n).
* Memory Complexity - Linear, O(n).
* */
public static void removeDuplicates1(char[] str){
Set<Character> hashSet = new LinkedHashSet<>();
int write_index = 0;
int read_index = 0;
while (str[read_index] != '\0') {
if(!hashSet.contains(str[read_index])) {
hashSet.add(str[read_index]);
str[write_index] = str[read_index];
++write_index;
}
++read_index;
}
str[write_index] = '\0';
}
// this solution does not require any extra memory
// but runs in O(n^2) time
// Null terminating strings are not used in Java.
// For this question, assume that you are passed a
// null terminated string (array of characters).
public static void removeDuplicates2(char[] str){
if(str == null || str.length == 0) {
return;
}
int write_index = 0;
for(int i = 0; i < str.length; i++) {
boolean found = false;
for(int j = 0; j < write_index; j++) {
if(str[i] == str[j]) {
found = true;
break;
}
}
if(!found) {
str[write_index] = str[i];
write_index++;
}
}
str[write_index] = '\0';
}
public static void main(String[] args) {
String string = "abbabcddbabcdeedebc";
System.out.println(removeDuplicates(string));
}
}