Binary Search Algorithm

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Fri Jan 03 2025 18:59:47 GMT+0000 (Coordinated Universal Time)

Saved by @khadizasultana #loop #c++ #vector #pointers #binarysearch 

// Author : Khadiza Sultana
// Date : 1/4/2025
#include<iostream>
#include<vector>
using namespace std;

int binarySearch(vector<int>&arr, int tar) { // practical implementation
    int n = arr.size();
    int st = 0, end = n-1;
    while(st <= end) {
        int mid = st + (end-st)/2; // not using (st+end)/2 to avoid integer overflow
        if (tar > arr[mid]) {
            st = mid+1;
        }
        else if (tar < arr[mid]) {
            end = mid-1;
        }
        else {
            return mid;
        }
    }
    return -1;
}

int binarySearch2(vector<int>&arr, int tar, int st, int end) { // recursive implementation
    if (st > end) { // base case
        return -1;
    }
    int mid = st + (end-st)/2;
    if (tar > arr[mid]) {
        binarySearch2(arr, tar, mid+1, end);
    }
    else if (tar < arr[mid]) {
        binarySearch2(arr, tar, st, mid-1);
    }
    else {
        return mid;
    }
}

int main() {
    vector<int>arr1 = {3, 5, 7, 12, 15, 18}; // even no of elements
    int tar1 = 3;
    vector<int>arr2 = {4, 6, 10, 11, 12, 18, 19}; // odd no of elements
    int tar2 = 19;

    cout << "Index at which tar1 is found(even no of elements) : " << binarySearch(arr1, tar1) << endl;
    cout << "Index at which tar2 is found(odd no of elements) : " << binarySearch(arr2, tar2) << endl;
    
    cout << "Using Recusive function index at which tar1 is found : " << binarySearch2(arr1, tar1, 0, 5) << endl;
    cout << "Using Recusive function index at which tar1 is found : " << binarySearch2(arr2, tar2, 0, 6) << endl;

    return 0;
}
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