2-D Arrays

Dynamically 2-D Array Allocation

int **arr = new int*[rows];
    for (int i = 0; i < rows; i++){
        arr[i] = new int[cols];
    }
// releasing memory 
    for (int i = 0; i < rows; i++){
        delete [] arr[i];
    }
    delete []arr;

Numbers of Rows & Columns in 2d

int arr[][3] = { { 1, 2, 3 },
                 { 4, 5, 6 },
                 { 7, 8, 9 } };
    
    int total_Elements = sizeof(arr)/sizeof(int); // 36 / 4 = 9
    cout << "Total Number of elements are: " << total_Elements << endl; 

    int rows = sizeof(arr)/sizeof(arr[0]);  // 36 / 12 = 3

    int cols = sizeof(arr[0])/sizeof(int);  // 12 / 4 = 3
    
    cout << "No of Rows are: "   << rows << endl;
    cout << "No of Columns are: "<< cols << endl;

if(largest < sum){
     largest = sum;
     largest_row/colum_index = i;
}

Q1: Row-Wise Sum

void RowWiseSum(int arr[][4], int row, int col){
    int largest = INT_MIN;

    cout << "Rows sum!!" << endl;
    for (int i = 0; i < row; i++){
        int sum = 0;
        for (int j = 0; j < col; j++){
            sum += arr[i][j];
        }
        largest = max(largest, sum);
    }
    cout << endl << "Largest Row Sum: " << largest << endl;
}

Q2: Column-Wise Sum

void ColWiseSum(int arr[][4], int row, int col){
    int largest = INT_MIN; 

    cout << "Columns sum!!" << endl;
    for (int i = 0; i < col; i++){
        int sum = 0;
        for (int j = 0; j < row; j++){
            sum += arr[j][i]; // arr[row][col];
        }
        largest = max(largest, sum);
    }
    cout << endl << "Largest Columns Sum: " << largest;
}

Q3: Print Like a Wave

Using vector

vector<int> wavePrint(vector<vector<int>> arr, int nRows, int mCols)
{
    vector <int> ans;
    for(int i = 0; i < mCols; i++){
        if(i%2 == 0) { 
            // top to bottom
            for (int j = 0; j < nRows; j++) {
                ans.push_back(arr[j][i]);
            }
        } 
        else {
            // bottom to top
            for (int j = nRows-1; j >= 0; j--) {
                ans.push_back(arr[j][i]);
            }
        }
    }
    return ans;
}

// T.C = O(nRows*mCols)

Using Array

#include <iostream>
using namespace std;

void print(int arr[][3], const int rows, const int cols) {
    for (int i = 0; i < cols; i++) {
        if(i%2 == 0) {
            for (int j = 0; j < rows; j++) {
                cout << arr[j][i] << " ";
            }
        }
        else{
            for (int j = rows-1; j >= 0; j--) {
                cout << arr[j][i] << " ";
            }
        }
    }
}

int main() {
    int arr[][3] = { { 1, 2, 3 },
                     { 4, 5, 6 },
                     { 7, 8, 9 } };
    int rows = sizeof(arr)/sizeof(arr[0]);
    int cols = sizeof(arr[0])/sizeof(int);
    print(arr, rows, cols); // 1 4 7 8 5 2 3 6 9
}

Q4: Spiral Matrix

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int>>& matrix) {
        
        int SR = 0;
        int SC = 0;
        
        int ER = matrix.size()-1;
        int EC = matrix[0].size()-1;
        
        int count = 0;
        int total = matrix.size() *  matrix[0].size();

        vector<int> ans; 

        while(count < total) {
        
            for(int i = SC; count < total && i <= EC; i++, count++) 
                ans.push_back(matrix[SR][i]);

            SR++;

            for(int i = SR; count < total && i <= ER; i++, count++) 
                ans.push_back(matrix[i][EC]);

            EC--;
            
            for(int i = EC; count < total && i >= SC; i--, count++) 
                ans.push_back(matrix[ER][i]);

            ER--;

            for(int i = ER; count < total && i >= SR; i--, count++) 
                ans.push_back(matrix[i][SC]);
            
            SC++;
        }
        return ans;
    }
};

Q5: Transpose of a Matrix

using single array

#include <iostream>
using namespace std;

int** transposeOFMatrix(int arr[][2], const int rows, const int cols) {
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < i; j++) { //  ignoring diagonals 
            swap(arr[i][j], arr[j][i]);
        }
    }
}

int main() {
    int arr[][2] = { {1, 2}, {3, 4}, {5, 6}};                     
    int rows = sizeof(arr)/sizeof(arr[0]);
    int cols = sizeof(arr[0])/sizeof(int);
    transposeOFMatrix(arr, rows, cols); 

    for (int i = 0; i < cols; i++) {
        for (int j = 0; j < rows; j++) {
            cout << arr[i][j] << " ";
        } cout << endl;
    }

    return 0;
}

phatt gya nahh hahaha

#include <iostream>
using namespace std;

int** transposeOFMatrix(int arr[][2], const int rows, const int cols) {
    
    int **temp = new int*[cols];
    *temp = new int[rows];

    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            temp[j][i] = arr[i][j];
        }
    }

    return temp;
}

int main() {
    int arr[][2] = { {1, 2}, {3, 4}, {5, 6}};
                     
    int rows = sizeof(arr)/sizeof(arr[0]);
    int cols = sizeof(arr[0])/sizeof(int);

   int **ptr = transposeOFMatrix(arr, rows, cols); 

    for (int i = 0; i < cols; i++) {
        for (int j = 0; j < rows; j++) {
            cout << ptr[i][j] << " ";
        } cout << endl;
    }

    // deallocating dynamic memory
    for (int i = 0; i < rows; i++) {
        delete[] ptr[i];
    }
    delete[] ptr;
    return 0;
}

Q6: Rotate Image

Dry Run

/*
   Steps to rotate image
      - Transpose matrix --> ignoring diagonal elements while swapping
      - Swap the columns
 */
#include <iostream>
using namespace std;

void rotateby90(int arr[][3], const int rows, const int cols) {
    
    // transpose
    for (int i = 0; i < 3; i++) {
    
        for (int j = 0; j < i; j++) { // ignoring diagonals index(0 0, 1 1, 2 2)
            swap(arr[i][j], arr[j][i]);
        }
    }
    
    // swap columns of each row
    for (int i = 0; i < rows; i++) {
        int s = 0;
        int e = cols-1;
        while (s <= e) {
            swap(arr[i][s++], arr[i][e--]);
        }
    }

}

int main() {
    int arr[][3] = { { 1, 2, 3 },
                     { 4, 5, 6 },
                     { 7, 8, 9 } };                
    int rows = sizeof(arr)/sizeof(arr[0]);
    int cols = sizeof(arr[0])/sizeof(int);

    rotateby90(arr, rows, cols); 
    
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            cout << arr[i][j] << " ";
        } cout << endl;   
    }   
}

Q7: Jagged Array

#include<iostream>
using namespace std;

const int MAX = 100;

int main(){
    int Rows;
    cout << "Rows: "; cin >> Rows;

    // creating 2-d array
    int **arr = new int *[Rows];
    int Cols[MAX];

    for (int i = 0; i < Rows; i++){
        cout << "Enter Colms for " << i+1 << ": "; cin >> i[Cols];
        arr[i] = new int[Cols[i]];
    }
    
    cout << "Enter Elements !!" << endl;
    for (int i = 0; i < Rows; i++){
        for (int j = 0; j < i[Cols]; j++){
            cin >> i[arr][j];
        }
    }
    
    cout << " Your Jagged Array!!" << endl;
    for (int i = 0; i < Rows; i++){
        for (int j = 0; j < i[Cols]; j++){
            cout << i[arr][j] << " "; 
        }cout << endl;
    }
}

Q8: Addition of 2 Matrix

#include <iostream>
using namespace std;

int** addition(int a[][2], int b[][2], int rows, int cols) {
    int **temp = new int*[rows];
    *temp = new int[cols];

    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            temp[i][j] = a[i][j] + b[i][j];
        }
    }
    return temp;
}

int main() {

    int a[2][2] = { { 1,  2}, 
                    {-1, -2} };
    int b[2][2] = { { 3,  4}, 
                    {-3, -4} };
    
    int** ptr = addition(a, b, 2, 2);

    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 2; j++) {
            cout << ptr[i][j] << " ";
        }cout << endl;
    }
    
    for (int i = 0; i < 2; i++) {
        delete[] ptr[i];
    }
    delete[] ptr;
    return 0;    
}

Q9: Multiplication of a matrix

#include <iostream>
using namespace std;

// Two matrices A and B are said to be conformable for the product AB if the number
// of columns of A is equal to the number of rows of B.

int main() {
    int a[][3] = { {1, 2, 3},
                   {4, 5, 6} };
    int b[][2] = { {1, 2},
                   {3, 4},
                   {5, 6} };
                   
    int c[2][2] = {0};

    for (int i = 0; i < 2; i++) {
        for (int k = 0; k < 2; k++){
            for (int j = 0; j < 3; j++) {
                c[i][k] += a[i][j] * b[j][k];
            }
        }
    }
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 2; j++) {
            cout << c[i][j] << " ";
        }cout << endl;
    }
    return 0;
}

Q10: Reverse 2d array

#include <iostream>
using namespace std;

int main() {
    int arr[][3] = { {1, 2, 3},
                     {4, 5, 6},
                     {7, 8, 9} };
                     
    int row = sizeof(arr)/sizeof(arr[0]);
    int col = sizeof(arr[0])/sizeof(int);
    
    for (int i = 0; i < row; i++) {
        int s = 0;
        int e = col-1;

        while (s <= e) {
            swap(arr[i][s++], arr[i][e--]);
        }
    }
    
    for (int i = 0; i < row; i++) {
        for (int j = 0; j < col; j++) {
            cout << arr[i][j] << " ";
        }cout << endl;
    }
    return 0;
}

Q11: Spiral Matrix II

class Solution {
public:
    vector<vector<int>> generateMatrix(int n) {
        int SR = 0;
        int SC = 0;
        
        int ER = n-1;
        int EC = n-1;
        
        int count = 1;
        int total = n*n;

        vector<vector<int>> matrix(n, vector<int>(n)); 
        
        while(count <= total) {

            for(int i = SC; count <= total && i <= EC; i++) 
                matrix[SR][i] = count++;
             
            SR++;

            for(int i = SR; count <= total && i <= ER; i++) 
                matrix[i][EC] = count++;
             
            EC--;
            
            for(int i = EC; count <= total && i >= SC; i--) 
                matrix[ER][i] = count++;
            
            ER--;
            
            for(int i = ER; count <= total && i >= SR; i--) 
                matrix[i][SC] =count++;
                
            SC++;
        }
        return matrix;
    }
};

Q12: Spiral Matrix IV

class Solution {
public:
    vector<vector<int>> spiralMatrix(int m, int n, ListNode* head) {
        int SR = 0;
        int SC = 0;
        
        int ER = m-1;
        int EC = n-1;

        vector<vector<int>> matrix(m, vector<int>(n, -1));
        
        while(head != nullptr) {

            for(int i = SC; head != nullptr && i <= EC; i++, head = head -> next) 
                matrix[SR][i] = head -> val;
            
            SR++;

            for(int i = SR; head != nullptr && i <= ER; i++, head = head -> next) 
                matrix[i][EC] = head -> val;
             
            EC--;
            
            for(int i = EC; head != nullptr&& i >= SC; i--, head = head -> next) 
                matrix[ER][i] = head -> val;

            ER--;
            
            for(int i = ER; head != nullptr && i >= SR; i--, head = head -> next) 
                matrix[i][SC] = head -> val;
            
            SC++;
        }
        return matrix;
    }
};