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GFG_EfficientFirstOccu.cpp

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+#include<bits/stdc++.h>
+using namespace std;
+
+// RECURSIVE 
+
+int find(int *arr,int low,int high, int x){
+	if(high<low){
+		return -1;
+	}
+	else{
+		int mid=(high+low)/2;
+		if(arr[mid]<x){
+			return find(arr,mid+1,high,x);
+		}
+		else if(arr[mid]>x){
+			return find(arr,low,mid-1,x);
+		}
+		else{
+			if(mid==0||(arr[mid]!=arr[mid-1])){
+				// cout<<"hello";
+				return mid;
+			}
+			else{
+				return find(arr,low,mid-1,x);
+			}
+		}
+	}
+}
+
+
+// ITERATIVE
+
+int findIterative(int *arr,int n,int x){
+	int low=0,high=n-1;
+	while(low<=high){
+		int mid=(low+high)/2;
+		if(arr[mid]<x){
+			low=mid+1;
+		}
+		else if (arr[mid]>x){
+			high=mid-1;
+		}
+		else{
+			if(mid==0||(arr[mid]!=arr[mid-1])){
+				return mid;
+			}
+			else{
+				high=mid-1;
+			}
+		}
+	}
+	return -1;
+}
+
+int findLastOccu(int *arr,int n,int x){
+	int low=0,high=n-1;
+	while(low<=high){
+		int mid=(low+high)/2;
+		if(arr[mid]<x){
+			low=mid+1;
+		}
+		else if (arr[mid]>x){
+			high=mid-1;
+		}
+		else{
+			if(mid==n-1||arr[mid]!=arr[mid+1]){
+				return mid;
+			}
+			else{
+				low=mid+1;
+			}
+		}
+	}
+	return -1;
+}
+
+int numberOccu(int *arr,int n,int x){
+	int first=findIterative(arr,n,x);
+	if(first==-1){
+		return 0;
+	}
+	else{
+		return (findLastOccu(arr,n,x)-first+1);
+	}
+}
+
+int main(){
+	int arr[]={10,10,15,20,20,20};
+	int n=6;
+	// cout<<find(arr,0,n,15);
+	cout<<findIterative(arr,n,10)<<endl;
+	cout<<findLastOccu(arr,n,15)<<endl;
+	cout<<numberOccu(arr,n,10);
+}