Ternary search.cpp

// this here is an iterative approach to ternary search 

#include <iostream> 
#include<bits/stdc++.h>
using namespace std; 

// Function to perform Ternary Search 
int ternarySearch(int l, int r, int key, int ar[]) 

{ 
    while (r >= l) { 

        // Find the mid1 and mid2 
        int mid1 = l + (r - l) / 3; 
        int mid2 = r - (r - l) / 3; 

        // Check if key is present at any mid 
        if (ar[mid1] == key) { 
            return mid1; 
        } 
        if (ar[mid2] == key) { 
            return mid2; 
        } 

        // Since key is not present at mid, 
        // check in which region it is present 
        // then repeat the Search operation 
        // in that region 

        if (key < ar[mid1]) { 

            // The key lies in between l and mid1 
            r = mid1 - 1; 
        } 
        else if (key > ar[mid2]) { 

            // The key lies in between mid2 and r 
            l = mid2 + 1; 
        } 
        else { 

            // The key lies in between mid1 and mid2 
            l = mid1 + 1; 
            r = mid2 - 1; 
        } 
    } 

    // Key not found 
    return -1; 
} 

// Driver code 
int main() 
{ 
    int l, r, p, key,n; 

    cin>>n; //enter the size of array to be inserted
    int a[n];
    for(int i=0;i<n;i++)
    cin>>a[i];

    sort(a,a+n);
    // Starting index 
    l = 0; 

    // length of array 
    r = n-1; 


    cin>>key; //key to be searched


    // Search the key using ternarySearch 
    p = ternarySearch(l, r, key, a); 

    // Print the result 
    cout << "Index of "<<key<<" is " << p << endl; 


}