Find the missing value from the given equation a + b = c

Given an equation of the form: 

a + b = c

Out of which any one of the terms , or is missing. The task is to find the missing term.

Examples:  

Input: 2 + 6 = ?
Output: 8

Input: ? + 3 =6
Output: 3

Approach: 

Missing numbers can be found simply using the equation . First, we will find two known numbers from the given equation(read as a string in the program) and convert them into integers, and put into the equation. In this way, we can find the third missing number. We can implement it by storing the equation into the string.

Below is the step by step algorithm: 

• Split the string into smaller strings from the position of spaces and store in an array. So that the array will contain:

arr[0] = "a"
arr[1] = "+"
arr[2] = "b"
arr[3] = "="
arr[4] = "c"

• The missing character can occur at position 0 or 2 or 4 in the vector. Find the position of missing character.
• Convert known characters to integers.
• Find missing character using the equation.

Below is the implementation of the above approach:  

C++

// C++ program to find the missing number
// in the equation a + b = c
#include <bits/stdc++.h>
using namespace std;

// Function to find the missing number
// in the equation a + b = c
int findMissing(string str)
{
    // Array of string to store individual strings
    // after splitting the strings from spaces
    string arrStr[5];

    // Using stringstream to read a string object
    // and split
    stringstream ss(str);

    int i = 0;

    while (ss.good() && i < 5) {
        ss >> arrStr[i];
        ++i;
    }

    int pos = -1;

    // Find position of missing character
    if(arrStr[0] == "?")
        pos = 0;
    else if(arrStr[2] == "?")
        pos = 2;
    else
        pos = 4;

    if(pos == 0)
    {
        string b,c;
        b = arrStr[2];
        c = arrStr[4];

        // Using stoi() to convert strings to int
        int a = stoi(c) - stoi(b);

        return a;
    }
    else if(pos==2)
    {
        string a,c;
        a = arrStr[0];
        c = arrStr[4];

        // Using stoi() to convert strings to int
        int b = stoi(c) - stoi(a);

        return b;
    }
    else if(pos == 4)
    {
        string b,a;
        a = arrStr[0];
        b = arrStr[2];

        // Using stoi() to convert strings to int
        int c = stoi(a) + stoi(b);

        return c;
    }
}

// Driver code
int main()
{
    // Equation with missing value
    string str = "? + 3 = 7";

    cout<<findMissing(str);

    return 0;
}

Java

// Java program to find the missing number
// in the equation a + b = c
import java.util.*;

class GFG{

// Function to find the missing number
// in the equation a + b = c
static int findMissing(String str)
{

    // Array of String to store individual
    // strings after splitting the strings
    // from spaces
    String arrStr[] = str.split(" ");

    int pos = -1;

    // Find position of missing character
    if (arrStr[0].equals("?"))
        pos = 0;
    else if (arrStr[2].equals("?"))
        pos = 2;
    else
        pos = 4;

    if (pos == 0)
    {
        String b, c;
        b = arrStr[2];
        c = arrStr[4];

        // Using Integer.parseInt() to
        // convert strings to int
        int a = Integer.parseInt(c) -
                Integer.parseInt(b);

        return a;
    }

    else if (pos == 2)
    {
        String a, c;
        a = arrStr[0];
        c = arrStr[4];

        // Using Integer.parseInt() to
        // convert strings to int
        int b = Integer.parseInt(c) -
                Integer.parseInt(a);

        return b;
    }

    else if (pos == 4)
    {
        String b, a;
        a = arrStr[0];
        b = arrStr[2];

        // Using Integer.parseInt() to
        // convert strings to int
        int c = Integer.parseInt(a) +
                Integer.parseInt(b);

        return c;
    }
    return 0;
}

// Driver code
public static void main(String []args)
{

    // Equation with missing value
    String str = "? + 3 = 7";

    System.out.print(findMissing(str));
}
}

// This code is contributed by pratham76

Python3

# Python3 program to find the missing number
# in the equation a + b = c

# Function to find the missing number
# in the equation a + b = c
def findMissing(s):

    # Array of string to store individual strings
    # after splitting the strings from spaces
    arrStr = s.split()

    # Using stringstream to read a string object
    # and split
    pos = -1;

    # Find position of missing character
    if(arrStr[0] == "?"):
        pos = 0;
    elif(arrStr[2] == "?"):
        pos = 2;
    else:
        pos = 4;

    if(pos == 0):

        b = arrStr[2];
        c = arrStr[4];

        # Using int() to convert strings to int
        a = int(c) - int(b);

        return a;

    elif(pos == 2):

        a = arrStr[0];
        c = arrStr[4];

        # Using int() to convert strings to int
        b = int(c) - int(a);

        return b;

    elif(pos == 4):

        a = arrStr[0];
        b = arrStr[2];

        # Using int() to convert strings to int
        c = int(a) + int(b);

        return c;

# Driver code
if __name__=='__main__':

    # Equation with missing value
    s = "? + 3 = 7";

    print(findMissing(s))

    # This code is contributed by rutvik_56

C#

// C# program to find the missing number
// in the equation a + b = c
using System;
class GFG
{

    // Function to find the missing number
    // in the equation a + b = c
    static int findMissing(string str)
    {

        // Array of String to store individual
        // strings after splitting the strings
        // from spaces
        string[] arrStr = str.Split(" ");
        int pos = -1;

        // Find position of missing character
        if (arrStr[0].Equals("?"))
            pos = 0;
        else if (arrStr[2].Equals("?"))
            pos = 2;
        else
            pos = 4;
        if (pos == 0)
        {
            string b, c;
            b = arrStr[2];
            c = arrStr[4];

            // Using Integer.parseInt() to
            // convert strings to int
            int a = int.Parse(c) - int.Parse(b);
            return a;
        }
        else if (pos == 2)
        {
            string a, c;
            a = arrStr[0];
            c = arrStr[4];

            // Using Integer.parseInt() to
            // convert strings to int
            int b = int.Parse(c) - int.Parse(a);
            return b;
        }

        else if (pos == 4)
        {
            string b, a;
            a = arrStr[0];
            b = arrStr[2];

            // Using Integer.parseInt() to
            // convert strings to int
            int c = int.Parse(a) + int.Parse(b);
            return c;
        }
        return 0;
    }

    // Driver code
    public static void Main(string[] args)
    {

        // Equation with missing value
        string str = "? + 3 = 7";
        Console.WriteLine(findMissing(str));
    }
}

// This code is contributed by chitranayal.

Javascript

<script>

// JavaScript program to find the missing number
// in the equation a + b = c

    // Function to find the missing number
// in the equation a + b = c
    function findMissing(str)
    {
        // Array of String to store individual
    // strings after splitting the strings
    // from spaces
    let arrStr = str.split(" ");

    let pos = -1;

    // Find position of missing character
    if (arrStr[0]==("?"))
        pos = 0;
    else if (arrStr[2]==("?"))
        pos = 2;
    else
        pos = 4;

    if (pos == 0)
    {
        let b, c;
        b = arrStr[2];
        c = arrStr[4];

        // Using Integer.parseInt() to
        // convert strings to int
        let a = parseInt(c) -
                parseInt(b);

        return a;
    }

    else if (pos == 2)
    {
        let a, c;
        a = arrStr[0];
        c = arrStr[4];

        // Using Integer.parseInt() to
        // convert strings to int
        let b = parseInt(c) -
                parseInt(a);

        return b;
    }

    else if (pos == 4)
    {
        let b, a;
        a = arrStr[0];
        b = arrStr[2];

        // Using Integer.parseInt() to
        // convert strings to int
        let c = parseInt(a) +
                parseInt(b);

        return c;
    }
    return 0;
    }

    // Driver code
    // Equation with missing value
    let str = "? + 3 = 7";
    document.write(findMissing(str));


// This code is contributed by rag2127

</script>

Output

4

Complexity Analysis:

• Time Complexity: O(1)
• Auxiliary Space: O(1)