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FirstLast.java
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FirstLast.java
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package searching;
public class FirstLast{
//if x is present in arr[] then
//returns the index of FIRST
//occurrence of x in arr[0..n-1],
//otherwise returns -1
static int first(int arr[],
int x, int n)
{
int low = 0, high = n - 1,
res = -1;
while (low <= high)
{
// Normal Binary Search Logic
int mid = (low + high) / 2;
if (arr[mid] > x)
high = mid - 1;
else if (arr[mid] < x)
low = mid + 1;
// If arr[mid] is same as
// x, we update res and
// move to the left half.
else
{
res = mid;
high = mid - 1;
}
}
return res;
}
//If x is present in arr[] then returns
//the index of LAST occurrence of x in
//arr[0..n-1], otherwise returns -1
static int last(int arr[], int x, int n)
{
int low = 0, high = n - 1,
res = -1;
while (low <= high)
{
// Normal Binary Search Logic
int mid = (low + high) / 2;
if (arr[mid] > x)
high = mid - 1;
else if (arr[mid] < x)
low = mid + 1;
// If arr[mid] is same as x,
// we update res and move to
// the right half.
else
{
res = mid;
low = mid + 1;
}
}
return res;
}
//Driver program
public static void main(String[] args)
{
int arr[] = {1, 2, 2, 2, 2,
3, 4, 7, 8, 8};
int n = arr.length;
int x = 8;
System.out.println("First Occurrence = " +
first(arr, x, n));
System.out.println("Last Occurrence = " +
last(arr, x, n));
}
}
//This code is contributed by Chitranayal