Convert a Mobile Numeric Keypad sequence to equivalent sentence

Given a string S of size N, consisting of digits [0 – 9] and character ‘.’, the task is to print the string that can be obtained by pressing the mobile keypad in the given sequence. 

Note: ‘.’ represents a break while typing.

Below is the image to represent the characters associated with each number in the keypad.

Examples:

Input: S = “234”
Output: ADG
Explanation:
Pressing the keys 2, 3, and 4 once gives the resultant string as “ADG”.

Input: S = “22.22”
Output: BB
Explanation:
Pressing the key 2 twice gives B, and then again pressing the key twice gives B. Therefore, the resultant string is “BB”.

Approach: The given problem can be solved by storing the mobile keypad mappings in an array and then traverse the string S and convert it into its equivalent string. Follow the steps below to solve the problem:

• Initialize an empty string, say ans to store the required result.
• Store the string associated to each key in the mobile keypad in an array nums[] such that nums[i] represent the set of characters on pressing the digit i.
• Traverse the given string S using the variable i and perform the following steps:
  • If S[i] is equal to ‘.’, then increment i by 1, and continue to the next iteration.
  • Otherwise, initialize a variable cnt as 0 to store the count of the same characters.
  • Iterate until S[i] is equal to S[i + 1] and in each iteration check the following conditions:
    • If cnt is equal to 2 and S[i] is 2, 3, 4, 5, 6, or 8, then break out of the loop because keys: 2, 3, 4, 5, 6, and 8 contain the same number of characters, i.e., 3.
    • If cnt is equal to 3 and S[i] is 7 or 9, then break out of the loop because keys: 7 and 9 contain the same number of characters, i.e., 4.
    • Increment the value of cnt and i by 1.
  • If S[i] is either 7 or 9, then add the character nums[str[i]][cnt%4] to the string ans.
  • Otherwise, add the character nums[str[i]][cnt%3] to the string ans.
  • Increment the value of i by 1.
• After completing the above steps, print the value string ans as the result.

Below is the implementation of the above approach:

C++

// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;

// Function to convert mobile numeric
// keypad sequence into its equivalent
// string
void printSentence(string str)
{
    // Store the mobile keypad mappings
    char nums[][5]
        = { "", "", "ABC", "DEF", "GHI",
            "JKL", "MNO", "PQRS", "TUV",
            "WXYZ" };

    // Traverse the string str
    int i = 0;
    while (str[i] != '\0') {

        // If the current character is
        // '.', then continue to the
        // next iteration
        if (str[i] == '.') {
            i++;
            continue;
        }

        // Stores the number of
        // continuous clicks
        int count = 0;

        // Iterate a loop to find the
        // count of same characters
        while (str[i + 1]
               && str[i] == str[i + 1]) {

            // 2, 3, 4, 5, 6 and 8 keys will
            // have maximum of 3 letters
            if (count == 2
                && ((str[i] >= '2'
                     && str[i] <= '6')
                    || (str[i] == '8')))
                break;

            // 7 and 9 keys will have
            // maximum of 4 keys
            else if (count == 3
                     && (str[i] == '7'
                         || str[i] == '9'))
                break;
            count++;
            i++;

            // Handle the end condition
            if (str[i] == '\0')
                break;
        }

        // Check if the current pressed
        // key is 7 or 9
        if (str[i] == '7' || str[i] == '9') {
            cout << nums[str[i] - 48][count % 4];
        }

        // Else, the key pressed is
        // either 2, 3, 4, 5, 6 or 8
        else {
            cout << nums[str[i] - 48][count % 3];
        }
        i++;
    }
}

// Driver Code
int main()
{
    string str = "234";
    printSentence(str);
    return 0;
}

Java

// java program for the above approach
import java.io.*;
import java.lang.*;
import java.util.*;

public class GFG {

    // Function to convert mobile numeric
    // keypad sequence into its equivalent
    // string
    static void printSentence(String S)
    {
        // Store the mobile keypad mappings
        String nums[]
            = { "",    "",    "ABC",  "DEF", "GHI",
                "JKL", "MNO", "PQRS", "TUV", "WXYZ" };

        char str[] = S.toCharArray();

        // Traverse the string str
        int i = 0;
        while (i < str.length) {

            // If the current character is
            // '.', then continue to the
            // next iteration
            if (str[i] == '.') {
                i++;
                continue;
            }

            // Stores the number of
            // continuous clicks
            int count = 0;

            // Iterate a loop to find the
            // count of same characters
            while (i + 1 < str.length
                   && str[i] == str[i + 1]) {

                // 2, 3, 4, 5, 6 and 8 keys will
                // have maximum of 3 letters
                if (count == 2
                    && ((str[i] >= '2' && str[i] <= '6')
                        || (str[i] == '8')))
                    break;

                // 7 and 9 keys will have
                // maximum of 4 keys
                else if (count == 3
                         && (str[i] == '7'
                             || str[i] == '9'))
                    break;
                count++;
                i++;

                // Handle the end condition
                if (i == str.length)
                    break;
            }

            // Check if the current pressed
            // key is 7 or 9
            if (str[i] == '7' || str[i] == '9') {
                System.out.print(
                    nums[str[i] - 48].charAt(count % 4));
            }

            // Else, the key pressed is
            // either 2, 3, 4, 5, 6 or 8
            else {
                System.out.print(
                    nums[str[i] - 48].charAt(count % 3));
            }
            i++;
        }
    }

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

        String str = "234";
        printSentence(str);
    }
}

// This code is contributed by Kingash.

Python3

# Python3 program for the above approach

# Function to convert mobile numeric
# keypad sequence into its equivalent
# string
def printSentence(str1):

    # Store the mobile keypad mappings
    nums = [ "", "", "ABC", "DEF", "GHI", "JKL",
             "MNO", "PQRS", "TUV", "WXYZ" ]

    # Traverse the string str1
    i = 0

    while (i < len(str1)):

        # If the current character is
        # '.', then continue to the
        # next iteration
        if (str1[i] == '.'):
            i += 1
            continue

        # Stores the number of
        # continuous clicks
        count = 0

        # Iterate a loop to find the
        # count of same characters
        while (i + 1 < len(str1) and str1[i + 1] and
                          str1[i] == str1[i + 1]):

            # 2, 3, 4, 5, 6 and 8 keys will
            # have maximum of 3 letters
            if (count == 2 and ((str1[i] >= '2' and
             str1[i] <= '6') or (str1[i] == '8'))):
                break

            # 7 and 9 keys will have
            # maximum of 4 keys
            elif (count == 3 and (str1[i] == '7' or
                                  str1[i] == '9')):
                break

            count += 1
            i += 1

            # Handle the end condition
            if (i < len(str)):
                break

        # Check if the current pressed
        # key is 7 or 9
        if (str1[i] == '7' or str1[i] == '9'):
            print(nums[ord(str1[i]) - 48][count % 4], end = "")

        # Else, the key pressed is
        # either 2, 3, 4, 5, 6 or 8
        else:
            print(nums[ord(str1[i]) - 48][count % 3], end = "")

        i += 1

# Driver Code
if __name__ == '__main__':

    str1 = "234"
    printSentence(str1)

# This code is contributed by bgangwar59

C#

// C# program for the above approach
using System;
public class GFG
{

    // Function to convert mobile numeric
    // keypad sequence into its equivalent
    // string
    static void printSentence(string S)
    {

        // Store the mobile keypad mappings
        string[] nums
            = { "",    "",    "ABC",  "DEF", "GHI",
                "JKL", "MNO", "PQRS", "TUV", "WXYZ" };

        char[] str = S.ToCharArray();

        // Traverse the string str
        int i = 0;
        while (i < str.Length) {

            // If the current character is
            // '.', then continue to the
            // next iteration
            if (str[i] == '.') {
                i++;
                continue;
            }

            // Stores the number of
            // continuous clicks
            int count = 0;

            // Iterate a loop to find the
            // count of same characters
            while (i + 1 < str.Length
                   && str[i] == str[i + 1]) {

                // 2, 3, 4, 5, 6 and 8 keys will
                // have maximum of 3 letters
                if (count == 2
                    && ((str[i] >= '2' && str[i] <= '6')
                        || (str[i] == '8')))
                    break;

                // 7 and 9 keys will have
                // maximum of 4 keys
                else if (count == 3
                         && (str[i] == '7'
                             || str[i] == '9'))
                    break;
                count++;
                i++;

                // Handle the end condition
                if (i == str.Length)
                    break;
            }

            // Check if the current pressed
            // key is 7 or 9
            if (str[i] == '7' || str[i] == '9') {
                Console.Write(nums[str[i] - 48][count % 4]);
            }

            // Else, the key pressed is
            // either 2, 3, 4, 5, 6 or 8
            else {
                Console.Write(nums[str[i] - 48][count % 3]);
            }
            i++;
        }
    }

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

        string str = "234";
        printSentence(str);
    }
}

// This code is contributed by ukasp.

Javascript

<script>

// Javascript program for the above approach

// Function to convert mobile numeric
// keypad sequence into its equivalent
// string
function printSentence(S)
{

    // Store the mobile keypad mappings
    let nums = [ "", "", "ABC", "DEF", "GHI",
                 "JKL", "MNO", "PQRS", "TUV", "WXYZ"];

    let str = S.split("");

    // Traverse the string str
    let i = 0;
    while (i < str.length)
    {

        // If the current character is
        // '.', then continue to the
        // next iteration
        if (str[i] == '.')
        {
            i++;
            continue;
        }

        // Stores the number of
        // continuous clicks
        let count = 0;

        // Iterate a loop to find the
        // count of same characters
        while (i + 1 < str.length &&
               str[i] == str[i + 1])
        {

            // 2, 3, 4, 5, 6 and 8 keys will
            // have maximum of 3 letters
            if (count == 2 && ((str[i] >= '2' &&
                str[i] <= '6') || (str[i] == '8')))
                break;

            // 7 and 9 keys will have
            // maximum of 4 keys
            else if (count == 3 && (str[i] == '7' ||
                                    str[i] == '9'))
                break;

            count++;
            i++;

            // Handle the end condition
            if (i == str.length)
                break;
        }

        // Check if the current pressed
        // key is 7 or 9
        if (str[i] == '7' || str[i] == '9')
        {
            document.write(
                nums[str[i].charCodeAt(0) - 48][count % 4]);
        }

        // Else, the key pressed is
        // either 2, 3, 4, 5, 6 or 8
        else
        {
            document.write(
                nums[str[i].charCodeAt(0) - 48][count % 3]);
        }
        i++;
    }
}

// Driver Code
let str = "234";

printSentence(str);

// This code is contributed by _saurabh_jaiswal.

</script>

Output:

ADG

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