Java Program to find the first duplicate occurence in an array

#learnwithkrishnasandeep #javacodinginterviewquestions #javaexamples #javaprograms #javatutorials #javaprogramming write a Java Program to find the first duplicate occurence in an array

In this video we are going to find out the first duplicate occurrence of a number in an array from given numbers.

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[sgh]

Since we are using nested loops, its a brute force technique where the complexity becomes O(n2), Instead we can use just one loop and store it in a HashMap and check whether the element encountered was second occurance or not.

[PathimelaArun]

It's time complexity is O(n^2). If this answer given in oracle... They will not consider at all

[mohammedajazquadri]

Instead of return you can use break directly we get first duplicate

[varunshrivastava]

public class DuplicateInArray {
public static void main(String[] args) {
int[] a = new int[] {1, 4, 2, 3, 1, 55, 6};
boolean flag;
Map<Integer, Integer> map = new HashMap<>();
for(int i=0;i<a.length;i++) {
if(map.containsKey(a[i])) {
System.out.println("The first duplicate in array is - " + a[i]);
flag=true;
}else {
map.put(a[i], 1);
}
}
if(!flag)
System.out.println("No duplicate found");
}
}

[Nodankumar]

If array is in order like..{1, 2, 3, 4, 3, 2, 4}...it prints 2...but by seeing an array we can say that 3 is 1st duplicated and then 2 ...but ur program op's 2 ..

[amanjainwal]

sir if add two duplicate value in array than it give all duplicate value not only first?

[chaitanyachundiwar]

if i give more duplicate numbers then it gives all those number but i need only 1st dubulicate
{1, 2, 3, 1, 4, 5, 4} it gives 1, 4 both but i need only 1

[HvujES]

you wrote O(N^2) this is bad you can do it with O(N) and cleaner
int[] arr=new int[]{1, 1, 1, 4, 4, 6, 7, 8, 9};


for(int i=0; i<str.length; i++){
int j=Math.abs(arr[i]);
if(arr[j]>=0)
arr[j]=-arr[j];
else
System.out.println(j+" ");

}

[abhimanyuchouhan]

when i run the code why only first number is always output even i have given duplicate number in array???

[venkateswararaopattapu]

public class FirstRepeatingElement1 {
public static void main(String[] args) {
int a[]= {1, 2, 3, 4, 5, 6, 1, 3};
boolean flag=false;
Map<Integer, Integer> map=new HashMap<Integer, Integer>();
for(int i=0;i<a.length;i++) {
if(map.containsKey(a[i])) {

break;

}else {
map.put(a[i], 1);
}
}
}
}