#include <iostream>
#include <vector>
#include <string>
using namespace std;

// Function to find the LCS
string findLCS(const string& str1, const string& str2) {
    int m = str1.length();
    int n = str2.length();

    // Initialize a 2D vector for dynamic programming
    vector<vector<int>> dp(m + 1, vector<int>(n + 1, 0));

    // Fill in the dp table
    for (int i = 1; i <= m; ++i) {
        for (int j = 1; j <= n; ++j) {
            if (str1[i - 1] == str2[j - 1])
                dp[i][j] = dp[i - 1][j - 1] + 1;
            else
                dp[i][j] = max(dp[i - 1][j], dp[i][j - 1]);
        }
    }

    // Reconstruct the LCS
    string lcs;
    int i = m, j = n;
    while (i > 0 && j > 0) {
        if (str1[i - 1] == str2[j - 1]) {
            lcs = str1[i - 1] + lcs;
            --i;
            --j;
        } else if (dp[i - 1][j] > dp[i][j - 1]) {
            --i;
        } else {
            --j;
        }
    }

    return lcs;
}

// Function to find the longest common substring
string findLongestCommonSubstring(const string& str1, const string& str2) {
    // Similar to LCS, but we only need the length
    int m = str1.length();
    int n = str2.length();
    vector<vector<int>> dp(m + 1, vector<int>(n + 1, 0));
    int maxLen = 0;
    int endIndex = 0;

    for (int i = 1; i <= m; ++i) {
        for (int j = 1; j <= n; ++j) {
            if (str1[i - 1] == str2[j - 1]) {
                dp[i][j] = dp[i - 1][j - 1] + 1;
                if (dp[i][j] > maxLen) {
                    maxLen = dp[i][j];
                    endIndex = i - 1;
                }
            }
        }
    }

    return str1.substr(endIndex - maxLen + 1, maxLen);
}

int main() {
    string str1, str2;
    cout << "Enter the first string: ";
    getline(cin, str1); // Read entire line (including spaces)
    cout << "Enter the second string: ";
    getline(cin, str2); // Read entire line (including spaces)

    // Find LCS
    string lcs = findLCS(str1, str2);
    cout << "Longest Common Subsequence (LCS): " << lcs << endl;
    cout << "Length of LCS: " << lcs.length() << endl;

    // Find longest common substring
    string commonSubstring = findLongestCommonSubstring(str1, str2);
    cout << "Longest Common Substring: " << commonSubstring << endl;
    cout << "Length of Common Substring: " << commonSubstring.length() << endl;

    return 0;
}
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Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}