binary search algorithm

1#include <iostream>
2using namespace std;
3
4// This program performs a binary search through an array, must be sorted to work
5int binarySearch(int array[], int size, int value) 
6{   
7    int first = 0,         // First array element       
8    last = size - 1,       // Last array element       
9    middle,                // Mid point of search       
10    position = -1;         // Position of search value   
11    bool found = false;        // Flag   
12    while (!found && first <= last) 
13    {      
14        middle = (first + last) / 2;     // Calculate mid point      
15        if (array[middle] == value)      // If value is found at mid      
16    	{         
17                found = true;         
18                position = middle;      
19        }      
20        else if (array[middle] > value)  // If value is in lower half         
21            last = middle - 1;      
22        else         
23            first = middle + 1;          // If value is in upper half   
24    }   
25    return position;
26}
27int main ()
28{
29    const int size = 5; // size initialization
30    int array[size] = {1, 2, 3, 4, 5}; // declare array of size 10
31    int value; // declare value to be searched for
32    int result; // declare variable that will be returned after binary search
33
34    cout << "What value would you like to search for? "; // prompt user to enter value
35    cin >> value;
36    result = binarySearch(array, size, value);
37
38    if (result == -1) // if value isn't found display this message
39        cout << "Not found\n";
40    else  // If value is found, displays message
41        cout << "Your value is in the array.\n"; 
42  
43    return 0;
44}

1// Java implementation of iterative Binary Search 
2class BinarySearch { 
3	// Returns index of x if it is present in arr[], 
4	// else return -1 
5	int binarySearch(int arr[], int x) 
6	{ 
7		int l = 0, r = arr.length - 1; 
8		while (l <= r) { 
9			int m = l + (r - l) / 2; 
10
11			// Check if x is present at mid 
12			if (arr[m] == x) 
13				return m; 
14
15			// If x greater, ignore left half 
16			if (arr[m] < x) 
17				l = m + 1; 
18
19			// If x is smaller, ignore right half 
20			else
21				r = m - 1; 
22		} 
23
24		// if we reach here, then element was 
25		// not present 
26		return -1; 
27	} 
28
29	// Driver method to test above 
30	public static void main(String args[]) 
31	{ 
32		BinarySearch ob = new BinarySearch(); 
33		int arr[] = { 2, 3, 4, 10, 40 }; 
34		int n = arr.length; 
35		int x = 10; 
36		int result = ob.binarySearch(arr, x); 
37		if (result == -1) 
38			System.out.println("Element not present"); 
39		else
40			System.out.println("Element found at "
41							+ "index " + result); 
42	} 
43} 

1#include<iostream>
2using namespace std;
3int binarySearch(int arr[], int p, int r, int num) {
4   if (p <= r) {
5      int mid = (p + r)/2;
6      if (arr[mid] == num)
7      return mid ;
8      if (arr[mid] > num)
9      return binarySearch(arr, p, mid-1, num);
10      if (arr[mid] > num)
11      return binarySearch(arr, mid+1, r, num);
12   }
13   return -1;
14}
15int main(void) {
16   int arr[] = {1, 3, 7, 15, 18, 20, 25, 33, 36, 40};
17   int n = sizeof(arr)/ sizeof(arr[0]);
18   int num = 33;
19   int index = binarySearch (arr, 0, n-1, num);
20   if(index == -1)
21   cout<< num <<" is not present in the array";
22   else
23   cout<< num <<" is present at index "<< index <<" in the array";
24   return 0;
25}

1#binary search python
2def binaryy(ar, ele):
3    low = 0 
4    high = len(ar)-1
5    if ele not in ar:
6        return "Not Found"
7    while low <= high:
8        mid = (low + high) // 2
9        if ar[mid] < ele:
10            low = mid + 1
11        elif ar[mid] > ele:
12            high = mid - 1
13        else:
14            return mid
15
16
17ar = [10, 20, 30, 40, 50]
18ele = 55
19print(binaryy(ar, ele))

1#include <bits/stdc++.h>
2using namespace std;
3
4int main(){
5    int n;
6    cin>>n;
7    vector<int>v(n);
8    for(int i = 0; i<n; i++){
9        cin>>v[i];
10    }
11    int to_find;
12    cin>>to_find;
13    int lo = 0 , hi = n-1 , mid ;
14    while(hi - lo > 1){
15        int mid = (hi + lo)/2;
16        if(v[mid] < to_find){
17            lo = mid + 1;
18        }else{
19            hi = mid;
20        }
21    }
22    if(v[lo] == to_find){
23        cout<<lo<<endl;
24    }else if(v[hi] == to_find){
25        cout<<hi<<endl;
26    }else{
27        cout<<"Not Found"; 
28    }
29
30    return 0;
31}

1#include <bits/stdc++.h>
2
3using namespace std;
4
5int binarySearch(int arr[], int l, int h, int key){
6    if(l<=h){
7        int mid = l + (h-l)/2;
8
9        if(arr[mid] == key){
10            return mid;
11        }
12
13        else if(arr[mid] > key){
14            return binarySearch(arr, l, mid-1, key);
15        }
16
17        else if(arr[mid] < key){
18            return binarySearch(arr,mid+1, h, key);
19        }
20    }       
21
22    return -1;
23}
24
25int main(){
26    int arr[] = {1,2,3,4,5,6,7,8,9,10};
27    int n = sizeof(arr)/sizeof(arr[0]);
28    int key = 7;
29
30    int result = binarySearch(arr,0,n-1,key);
31
32    (result==-1)
33        ? cout << "Element is not found in the array" << endl
34        : cout << "Element is found at index " << result;
35
36    return 0;
37
38}