// Efficient Code (Iterative)
import java.util.*;
import java.io.*;
class GFG
{
static int firstOcc(int arr[], int n, int x)
{
int low = 0, high = n - 1;
while(low <= high)
{
int mid = (low + high) / 2;
if(x > arr[mid])
low = mid + 1;
else if(x < arr[mid])
high = mid - 1;
else
{
if(mid == 0 || arr[mid - 1] != arr[mid])
return mid;
else
high = mid - 1;
}
}
return -1;
}
public static void main(String args[])
{
int arr[] = {5, 10, 10, 10, 20}, n = 5;
int x = 10;
System.out.println(firstOcc(arr, n, x)); // OUTPUT : 1
}
}
// Efficient Code (Recursive)
import java.util.*;
import java.io.*;
class GFG
{
static int firstOcc(int arr[], int low, int high, int x)
{
if(low > high)
return -1;
int mid = (low + high) / 2;
if(x > arr[mid])
return firstOcc(arr, mid + 1, high, x);
else if(x < arr[mid])
return firstOcc(arr, low, mid - 1, x);
else
{
if(mid == 0 || arr[mid - 1] != arr[mid])
return mid;
else
return firstOcc(arr, low, mid - 1, x);
}
}
public static void main(String args[])
{
int arr[] = {5, 10, 10, 15, 20, 20, 20}, n = 7;
int x = 20;
System.out.println(firstOcc(arr, 0, n - 1, x)); // OUTPUT : 4
}
}
// Naive Code
import java.util.*;
import java.io.*;
class GFG
{
static int firstOccurrence(int arr[], int n, int x)
{
for(int i = 0; i < n; i++)
if(arr[i] == x)
return i;
return -1;
}
public static void main(String args[])
{
int arr[] = {5, 10, 10, 15, 15}, n = 5;
int x = 15;
System.out.println(firstOccurrence(arr, n, x)); // OUTPUT : 3
}
}