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Count subarrays with all elements greater than K in C++
We are given an array arr[] of integers. Also a number K. The goal is to count all subarrays of arr[] such that all elements of the subarray are greater than K or K is less than all elements of the subarrays. If the array is [1,2,3] and K is 1. Subarrays will be [2], [3], [2,3].
Let us understand with examples.
Input − arr[] = { 2, 2, 1, 1, 1, 5 }; K=1
Output − Count of subarrays with all elements greater than K are − 4
Explanation − Subaarays will be: [2], [2], [5], [2,2]. All elements in each subarray are greater than 1.
Input − arr[] = { 3,4,5,6 }; K=2
Output − Count of subarrays with all elements greater than K are − 10
Explanation − Subaarays will be − [3], [4], [5], [6], [3,4], [4,5], [5,6], [3,4,5], [4,5,6], [3,4,5,6]. Total count=10.
The approach used in the below program is as follows
We will traverse the array using a for a loop. If the current element is greater than K. Increment count. Otherwise set count=0 and total=count*(count+1)/2. (for subarrays). If at the end count is non-zero. Add count*(count+1)/2 for a count of remaining subarrays.
Take an array arr[] of numbers.
Function sub_greater_k(int arr[], int size, int k) takes the array and returns a count of subarrays with all elements greater than k.
Take the initial count as 0.
We will traverse the array using for loops from i=0 to i<size.
If arr[i]>k then increment count.
Subarrays with count (elements > k ) will be count*(count+1)/2. Add this to the total for all such subarrays.
At the end of again add count*(count+1)/2 to total if the count is non-zero.
Return total as result.
Example
#include <bits/stdc++.h>
using namespace std;
int sub_greater_k(int arr[], int size, int k){
int count = 0;
int total = 0;
for (int i = 0; i < size; i++){
if (arr[i] > k){
count++;
}
else{
total += (count) * (count + 1) / 2;
count = 0;
}
}
if(count){
total += (count) * (count + 1) / 2;
}
return total;
}
int main(){
int arr[] = {2, 4, 6, 1, 3, 7, 9 };
int size = sizeof(arr) / sizeof(arr[0]);
int k = 7;
cout<<"Count of subarrays with all elements greater than K are: "<<sub_greater_k(arr, size, k);
return 0;
}Output
If we run the above code it will generate the following output −
Count of subarrays with all elements greater than K are: 1
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