/* Count Element Occurrence */
/*
Given a sorted array of integers, find the number of occurrences of a given target value.
Your algorithm’s runtime complexity must be in the order of O(log n). If the target is not found in the array, return 0
**Example : **
Given [5, 7, 7, 8, 8, 10] and target value 8, return 2.
*/
/*
Given a sorted array of integers, find the number of occurrences of a given target value.
Your algorithm’s runtime complexity must be in the order of O(log n). If the target is not found in the array, return 0
**Example : **
Given [5, 7, 7, 8, 8, 10] and target value 8, return 2.
*/
#include<iostream>
using namespace std;
int first(int *arr, int low, int high, int x){
int mid;
if(low > high){
return -1;
}
mid = low + (high - low) / 2;
if(arr[mid] == x && ((mid - 1) >= low && arr[mid - 1] < x)){
return mid;
} else if(arr[mid] > x){
return first(arr, 0, mid - 1, x);
}else{
return first(arr, mid + 1, high, x);
}
}
int last(int *arr, int low, int high, int x){
int mid;
if(low > high){
return -1;
}
mid = low + (high - low) / 2;
if(arr[mid] == x && ((mid + 1) <= high && arr[mid + 1] > x)){
return mid;
} else if(arr[mid] > x){
return first(arr, 0, mid - 1, x);
}else{
return first(arr, mid + 1, high, x);
}
}
int countOccurrences(int *arr, int n, int x){
int firstIndex = first(arr, 0, n - 1, x);
int lastIndex = last(arr, 0, n - 1, x);
cout << firstIndex << " " << lastIndex << endl;
//Element not found
if(firstIndex == -1){
return 0;
}
return lastIndex - firstIndex + 1;
}
int main(){
//int arr[] = {5, 7, 7, 7, 8, 8, 10};
int arr[] = {1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 4, 4, 5, 5, 5, 5, 5, 6, 6, 6, 7, 7, 8, 8, 8, 8, 9, 9, 10, 10, 10};
cout << countOccurrences(arr, sizeof(arr) / sizeof(arr[0]), 1);
return 0;
}
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