/* 
001 Two Number Sum

Write a function that takes in a non-empty array of distinct integers and an integer representing a target sum. If any two numbers in the input array sum up to the target sum, the function should return them in an array, in any order. If no two numbers sum up to the target sum, the function should return an empty array.

Note that the target sum has to be obtained by summing two different integer in the array; you can't add a single integer to itself in order to obtain the target sum.

You can assume that there will be at most one pair of numbers summing up to the target sum.

Sample Input
array = [3, 5, -4, 8, 11, 1, -1, 6]
targetSum = 10

Sample Output
(the numbers could be in reversed order)
[-1, 11]
*/

#include <vector>
#include <unordered_set>
#include <iostream>
#include <algorithm>

using namespace std;

// O(n) time | O(n) space
vector<int> twoNumberSum(vector<int> inputArray, int targetSum) {
  unordered_set<int> nums;
  for (int num: inputArray) {
    int potentialMatch = targetSum - num;
    if (nums.find(potentialMatch) != nums.end()) {      return vector<int>{potentialMatch, num};
    } else {
      nums.insert(num);
    }
  }
  return {};
}

// test
int main(int argc, char** argv) {
  int targetSum = 10;
  vector<int> inputArray = {3, 5, -4, 8, 11, 1, -1, 6};
  vector<int> outputArray = twoNumberSum(inputArray, targetSum);
  bool sizeCheck = outputArray.size() == 2;
  bool memberCheck1 = count(outputArray.begin(), outputArray.end(), -1);
  bool memberCheck2 = count(outputArray.begin(), outputArray.end(), 11);
  cout << boolalpha << sizeCheck << endl
       << memberCheck1 << endl
       << memberCheck2 << endl;

  // end of main func
  return 0;
}

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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
}