Answer to Question #121699 in C++ for Ethel omelanga

Question

Compression Algorithm:
One method of compressing a file is to recognize repeated digits and replace the runs of
repetition with a number representing the repetition length. For instance for a line in you file
such as ;
0110000000000110
Can be represented with the line:
1 2 10 2 1
Because there is 1 zero, 2 ones, 10 zeros, 2 ones and 1 zero. It is already understood that only
zeros and ones appear and that zeros apper first in a given line. Thus storing the new line of
data is much shorter (5 numbers) than the original line (16 numbers)
To decompress the encoded file you can follow the reverse implementation of the method
stated above, for example for the encoded data:
4 2 4 2 4
The decompressed data is:
0000110000110000

Answer 1

#include<bits/stdc++.h>
#include <xstring>
#include <iostream>

using namespace std;
//Global array to store the 0 or 1 in multidimentional array.
int arr[100][100];

/* It converts the integer to its corresponding string value.
 * Like 123 converted to "123".
 * @param: num, the number you want to convert into string. @return: string */
string toString(int num) {
    /* It is just maping of single integer to its corresponding character value. */
    vector<char> map = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};
    string convertedString = ""; /* Taking modulo of num and adding its corresponding character value into the right side of convertedString. */
    while (
            num > 0) {
        convertedString = map[num % 10] + convertedString;
        num = num / 10;
    }
    return convertedString;
}
/* It converts the integer string to its corresponding integer. 
 * Like "123" converted to 123. 
 * @param: str, it is the string value integer which you want to convert. 
 * @return: int */
int toInteger(
        string str) {
    int result = 0;
    //Value to be multiplied

    int power = 1;
    //Traverse the string in reverse order and multiply with
    // power of 10 everytime like str = "123", then
    // first 3 will be multiplied with 1, then 2 with 10,
    // and 1 with 100. Result will be result = 1x100 + 2x10 + 3x1 = 123.
    for (int i = str.size() - 1; i >= 0; i--) {
        result += power * (str[i] - '0');
        power *= 10;
    }
    return result;
} /* encodeRow is a function to encode a particular row of multidimentional array.
 * @param: arrRow[], one row of arr[][] containing 0 or 1. 
 * @param: size, It is the size of arrRow[]. @return: string of encoded values. */
string encodeRow(int arrRow[], int size) {
    string result = "";
    // cnt0 and cnt1 are counts of 0 and 1.
    int cnt0 = 0, cnt1 = 0;
    /* First you encounter 0 and keep incrementing you cnt0, when you encounter 1 
     * i.e, you are done with the count of 0, add cnt0 to your result string in string format do and make cnt0=0.
     * Do the same for 1 and repeat. At the end you will get you encoded string. 
     * One thing to note that you should not add any count of 0 or 1 to your result,
     * when your count is zero that is why that if statement is required. */
    for (int i = 0; i < size; i++) {
        if (arrRow[i] == 0) {
            if (cnt1 > 0) {
                result += toString(cnt1) + " ";
                cnt1 = 0;
            }
            cnt0++;
        } else {
            if (cnt0 > 0) {
                result += toString(cnt0) + " ";
                cnt0 = 0;
            }
            cnt1++;
        }
    }
    if (cnt0 > 0) result += toString(cnt0) + " ";
    if (cnt1 > 0) result += toString(cnt1) + " ";
    return result;
} /* This is the function to encode all your data. 
 * @param: row, number of rows in the array arr. 
 * @param: col, number of columns in the array arr. 
 * @return: None, it just print the encoded string. */
void encoding(int row, int col) {
    for (int i = 0; i < row; i++) {
        cout << encodeRow(arr[i], col) << endl;
    }
}

/* This function is for decoding a single string or row. 
 * It just take the encoded string as input and decode it.
 * @param: str, encoded string from compresed.txt, only one line. */
string decodingRow(string str) {
    string result = "";
    //Flag which tell us what to print 0 or 1.
    // By defaut it is set to zero.

    int flag = 0;
    string num = "";
    /* See we can have encoded string like 1 2 10 2 1. 
     * We need to store the every number into num string like num = "1", then num="2", then num = "10" and so on. 
     * After that we are converting it into integer using toInteger function. 
     * If the flag is zero add 0 to toInteger(num) times else add 1 toInteger(num) times to result string.
     * After every addition we are changing the flag using xor operation. */
    for (char ch : str) {
        if (ch !=' ') { // "10" having two characters that is why we are adding
            // adding ch into num everytime.
            num += ch;
        } else {
            if (flag == 0) {
                for (int i = 0; i < toInteger(num); i++) result += '0';
                flag ^= 1;
            } else {
                for (int i = 0; i < toInteger(num); i++) result += '1';
                flag ^= 1;
            }
            num = "";
        }
    }
    if (flag == 1) for (int i = 0; i < toInteger(num); i++) result += '1';
    if (flag == 0) for (int i = 0; i < toInteger(num); i++) result += '0';
    return result;
}

int main() {
    int option;
    cout << "1 for encoding && 2 for decoding." << endl;
    cout << "Enter your choice: ";
    cin
            >> option;
    //Encoding operation
    if (option == 1) {
        freopen("data.txt", "r",
                stdin);

        freopen("compresed.txt", "w", stdout);
        string str;
        int row = 0, col = 0;
        //getline function is used to read line. 

        while (getline(cin, str)) {
            col = str.size();
            for (int i = 0; i < col; i++) { arr[row][i] = str[i] - '0'; }
            row++;
        }
        encoding(row, col);
    } else {
        //Decoding operation 
        freopen("compresed.txt", "r", stdin);
        string str;
        while (getline(cin, str)) { cout << decodingRow(str) << endl; }
    }
    return 0;
}