(algorithm: Binary lookup) in a sorted array, to find out the number of occurrences of a given number

Topic:

In the sorted array, find out the number of occurrences of a given number

Ideas:

Since there is a sort array, it is easy to think of binary lookups, with time complexity O (LOGN);

First, by binary find the leftmost occurrence of the number of the subscript left (if not found, then return-1), and then through the binary search find the rightmost occurrence of the number of the following table right (if not found, then return-1), and then right-left+1 is the number of occurrences;

Code:

#include <iostream>using namespace Std;int binarysearchcount (int *array,int len,int data) {if (len<1) return-1    ;    int left=0;    int right=len-1;    int mid;    int leftindex=-1;        Find the left index while (left<=right) {mid=left+ ((right-left) >>1);            if (array[mid]==data) {leftindex=mid;        Right=mid-1;        } else if (array[mid]<data) left=mid+1;    else right=mid-1;    }//Find the right index left=0;    right=len-1;    int rightindex=-1;        while (left<=right) {mid=left+ ((right-left) >>1);            if (array[mid]==data) {rightindex=mid;        left=mid+1;        } else if (array[mid]<data) left=mid+1;    else right=mid-1;    } if (Leftindex!=-1 && rightindex!=-1) return rightindex-leftindex+1; else return 0;}    int main () {int arr[]={0,1,2,3,3,3,3,3,3,3,4,5,6,7,13,19}; int len=sizeof (arr)/sizEOF (Arr[0]);    cout << Binarysearchcount (arr,len,18) << Endl; return 0;}

(algorithm: Binary lookup) in a sorted array, to find out the number of occurrences of a given number