#include <iostream>
#include <unordered_map> 
#include <vector>
using namespace std;
class Solution {
public:
    vector<int> twoSumBF(vector<int>& nums, int target) {
        // Step 1: Iterate over the numbers in the array.
        for (int i = 0; i < nums.size(); i++) {
            // Step 2: For each number, iterate over the rest of the numbers in the array.
            for (int j = i + 1; j < nums.size(); j++) {
                // Step 3: Check if the current two numbers add up to the target.
                if (nums[i] + nums[j] == target) {
                    return {i, j};
                }
            }
        }
        // Step 4: If no such pair is found, return an empty vector.
        return {};
    }
    vector<int> twoSum2Pass(vector<int>& nums, int target) {
        // Step 1: Create a map to store numbers and their indices.
        unordered_map<int, int> numMap;
        // Step 2: Add each number and its index to the map.
        for (int i = 0; i < nums.size(); i++) {
            numMap[nums[i]] = i;
        }
        // Step 3: Check for each number, if its complement exists in the map.
        for (int i = 0; i < nums.size(); i++) {
            int complement = target - nums[i];
            // Ensure the complement is not the number itself.
            if (numMap.count(complement) && numMap[complement] != i) {
                // Step 4: If the complement exists, the indices are returned.
                return {i, numMap[complement]};
            }
        }
        // Step 5: If no two numbers sum up to the target, return an empty vector.
        return {};
    }
    vector<int> twoSum1Pass(vector<int>& nums, int target) {
        // Step 1: Again, create a map to store numbers and their indices.
        unordered_map<int, int> numMap;
        // Step 2: During iteration over the numbers, the complement is calculated for each number.
        for (int i = 0; i < nums.size(); i++) {
            int complement = target - nums[i];
            // Step 3: It checks if the complement exists in the map. If so, the indices are returned.
            if (numMap.count(complement)) {
                return {numMap[complement], i};
            }
            // Step 4: Otherwise, the current number and its index are added to the map.
            numMap[nums[i]] = i;
        }
        // Step 5: If no pair sums up to the target, return an empty vector.
        return {};
    }
};

int main(){
    Solution s ;
    vector<int> v;
     v={1,6,3,2,5};
     vector<int> result= s.twoSumBF(v, 11);
     cout<<"Brute Force Solution"<<endl;
     for(int i: result)
     {
          cout<<i<<endl;
     }
     result= s.twoSum2Pass(v, 11);
     cout<<"Two Pass Solution"<<endl;
     for(int i: result)
     {
          cout<<i<<endl;
     }
     result= s.twoSum1Pass(v, 11);
     cout<<"One Pass Solution"<<endl;
     for(int i: result)
     {
          cout<<i<<endl;
     }
     return 0;

}
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#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
}