C++ Program For Linear Search
Linear search algorithm is the simplest searching algorithm that is used to find an element in the given collection. It simply compares the element to find with each element in the collection one by one till the matching element is found or there are no elements left to compare.
In this article, we will learn about linear search algorithm and how to implement it in C++.
Linear Search Using Library Function
C++ STL provides the std::find() function that implements the linear search algorithm to find an element in some container or array. This function returns the pointer/iterator to the element if found, otherwise, it returns the pointer/iterator to the end.
Note: std::find() function performs linear search with arrays, vectors and lists. For ordered and unordered data containers such as map, unordered_map, etc. it searches for the given element according to the search performance of the container.
// C++ program to implement linear search using
// std::find() function
#include <bits/stdc++.h>
using namespace std;
int main() {
vector<int> v = {1, 2, 3, 4, 5, 8, 9, 11};
// Element to be searched
int key = 8;
// Searching for key in the vector v
auto it = find(v.begin(), v.end(), key);
// Checking if element is found or not
if (it != v.end())
cout << key << " Found at Position: " <<
it - v.begin() + 1;
else
cout << key << " NOT found.";
return 0;
}
Output
30 Found at Position: 3
Time Complexity: O(n), where n is the number of elements
Auxiliary Space: Implementation defined, discussed below
Manually Implement Linear Search in C++
We can also manually implement the linear search in C++ by using both iteration and recursion. But first, we need to understand the working of linear search:
Working of Linear Search
The working of linear search is simple. We compare the element to find with each element in the given collection one by one starting from the first element. If the element is found, we return its index and stop the search. Otherwise, if we reach the end of the collection without finding the element, we return some other value denoting that the element is not found in the given collection.
Iterative Implementation
// C++ Program to implement linear search
// algorithm iteratively
#include <bits/stdc++.h>
using namespace std;
int linearSearch(vector<int> v, int key) {
// We test all the elements of the vector
// v against the given key
for (int i = 0; i < v.size(); i++) {
// If the KEY IS FOUND
if (v[i] == key) {
return i;
}
}
// Return some value denoting KEY NOT FOUND
return -1;
}
int main() {
vector<int> v = {1, 2, 3, 4, 5, 8, 9, 11};
// Value to search
int key = 8;
// Searching the key in the vector v
int i = linearSearch(v, key);
// Checking if element is found or not
if (i != -1)
cout << key << " Found at Position: " <<
i + 1;
else
cout << key << " NOT found.";
return 0;
}
Output
6
Time Complexity: O(n), where n is the number of elements
Auxiliary Space: O(1)
Recursive Implementation
// C++ Program to implement linear search using
// recursion
#include <bits/stdc++.h>
using namespace std;
int linearSearch(vector<int>& v, int key, int i) {
// If we have traversed the entire vector
// and the key is not found
if (i == v.size()) {
return -1;
}
// If the current element matches the key
if (v[i] == key) {
return i;
}
// Recursive call to check the next element
return linearSearch(v, key, i + 1);
}
int main() {
vector<int> v = {1, 2, 3, 4, 5, 8, 9, 11};
// Value to search
int key = 8;
// Searching the key in the vector v
int i = linearSearch(v, key, 0);
// Checking if element is found or not
if (i != -1) {
cout << key << " Found at Position: "
<< i + 1;
} else {
cout << key << " NOT found.";
}
return 0;
}
Output
8 Found at Position: 6
Time Complexity: O(n), where n is the number of elements
Auxiliary Space: O(n), for recursion stack.
