cpp binary search code example

Example 1: how to do binary search in c++ using STL

// BY shivam kumar KIIT
#include<bits/stdc++.h>
usind namespace std;
int main()
{
	int arr[]={10,2,34,2,5,4,1};
  	sort(arr,arr+7);//sort array in ascending order before using binary search
  	binary_search(arr,arr+7,10);//return 1 as element is found
  	binary_search(arr,arr+7,3);//return 0 as element is not found
  	return 0;
}

Example 2: binary search function in c++

#include<iostream>
using namespace std;
int binarySearch(int arr[], int p, int r, int num) {
   if (p <= r) {
      int mid = (p + r)/2;
      if (arr[mid] == num)
      return mid ;
      if (arr[mid] > num)
      return binarySearch(arr, p, mid-1, num);
      if (arr[mid] > num)
      return binarySearch(arr, mid+1, r, num);
   }
   return -1;
}
int main(void) {
   int arr[] = {1, 3, 7, 15, 18, 20, 25, 33, 36, 40};
   int n = sizeof(arr)/ sizeof(arr[0]);
   int num = 33;
   int index = binarySearch (arr, 0, n-1, num);
   if(index == -1)
   cout<< num <<" is not present in the array";
   else
   cout<< num <<" is present at index "<< index <<" in the array";
   return 0;
}

Example 3: c++ binary search

//requires header <algorithm> for std::binary_search
#include <algorithm>
#include <vector>

bool binarySearchVector(const std::vector<int>& vector,
                       	int target) {
  //this line does all binary searching
  return std::binary_search(vector.cbegin(), vector.cend(), target);
}

#include <iostream>

int main()
{
    std::vector<int> haystack {1, 3, 4, 5, 9};
    std::vector<int> needles {1, 2, 3};
 
    for (auto needle : needles) {
        std::cout << "Searching for " << needle << std::endl;
        if (binarySearchVector(haystack, needle)) {
            std::cout << "Found " << needle << std::endl;
        } else {
            std::cout << "no dice!" << std::endl;
        }
    }
}

Example 4: Binary search in c++

//By Sudhanshu Sharan
#include<iostream>
#include<cmath>
using namespace std;
// BCT= o(1)  and  WCT=O(logn)   time taken for unsucessful search is always o(logn)

int BinSearch( int arr[],int key,int len)
{
	int h,mid,l;
	l=0;
	h=len-1;
	while(l<=h)
	{
		mid=((l+h)/2);
		if(key==arr[mid])
			return mid;
		else if(key<arr[mid])
			h=mid-1;
		else
			l=mid+1;
	}
	return -1;
}
int main()
{
	int key,i,len;
	int arr[] = {1,2,3,6,9,12,15,34,54};
	len=sizeof(arr)/sizeof(arr[0]);
	cout<<"enter the key to be searched";
	cin>>key;
	int result= BinSearch(arr,key,len);
	(result == -1)
		? cout<<"Element is not present in the array"<<endl
		: cout<<"Element is present at index : "<<result<<endl;	
	for(i=0;i<len-1;i++)
		cout<<arr[i]<<" ";
    return 0;
}

Example 5: c++ binary search

int result = -1;
  int low = 0;
  int high = N-1; // N - # of elements
   while (low <= high)
   {  mid = (low + high) / 2;
      if ( item == vector[mid])
	  {  result = mid;
	     break; 
      }
      else if (item > vector[mid] )
	           { low =  mid + 1; }
          else  { high = mid - 1; }
   }