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Convert a Mobile Numeric Keypad sequence to equivalent sentence
• Last Updated : 04 May, 2021

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”
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 using namespace std; // Function to convert mobile numeric// keypad sequence into its equivalent// stringvoid 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 Codeint main(){    string str = "234";    printSentence(str);    return 0;}

## Java

 // java program for the above approachimport 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.

## C#

 // C# program for the above approachusing 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.
Output: