Find alphabet in a Matrix which has maximum number of stars around it

11 Aug, 2021
Given a matrix mat consisting of * and lowercase English alphabets, the task is to find the character which has the maximum number of * around it (including diagonal elements too). If two characters have same maximum count, print lexicographically smallest character.Source :D-E Shaw Interview ExperienceExamples:  
Input: 
mat[][] = {{'b', '*', '*', '*'}, 
           {'*', '*', 'c', '*'}, 
           {'*', 'a', '*', '*'}, 
           {'*', '*', '*', 'd'}}
Output: a
'a', 'b', 'c' and 'd' are surrounded by 
'7', '3', '7' and '3' stars respectively.
'a' and 'c' are surrounded by maximum stars 
but 'a' is lexicographically smaller than 'c'.

Input: 
mat[][] = {{'*', 'r', '*', '*'}, 
           {'m', 'a', 'z', '*'}, 
           {'l', '*', 'f', 'k'}, 
           {'*', '*', '*', 'd'} }
Output: f
 
Approach: The idea is to traverse the matrix and if a character is found then calculate the count of stars around it. Check at all 8 positions around it and count the number of starts.Use a map to keep track of the character and the number of stars surrounding it. Then traverse the map and find the character which is surrounded by maximum stars and is lexicographically smallest.Below is the implementation of the above approach:  
C++
Java
Python3
C#
Javascript
// C++ program to find alphabet in a Matrix// which has maximum number of stars// surrounding it#include <bits/stdc++.h>using namespace std; // Function to return the count of stars// around a particular indexint countStars(int mat[][4], int i, int j, int n){    int count = 0;     int rowNum[] = { -1, -1, -1, 0, 0, 1, 1, 1 };    int colNum[] = { -1, 0, 1, -1, 1, -1, 0, 1 };     // consider all 8 neighbours    for (int k = 0; k < 8; k++) {        int x = i + rowNum[k];        int y = j + colNum[k];        if (x >= 0 && x < n && y >= 0 && y < n            && mat[x][y] == '*')            count++;    }     return count;} // Function to return the character in a Matrix// which has maximum number of stars around itchar alphabetWithMaxStars(int mat[][4], int n){    unordered_map<char, int> umap;     for (int i = 0; i < n; i++) {        for (int j = 0; j < n; j++) {             // If current element is a character            if ((mat[i][j] - 97) >= 0                && (mat[i][j] - 97) < 26) {                // Count of start surrounding it                int stars = countStars(mat, i, j, n);                umap[mat[i][j]] = stars;            }        }    }     int max = -1;    char result = 'z' + 1;     // Traverse the map    for (auto x : umap) {        if (x.second > max || (x.second == max                               && x.first < result)) {            max = x.second;            result = x.first;        }    }     return result;} // Driver codeint main(){    int mat[][4] = { { 'b', '*', '*', '*' },                     { '*', '*', 'c', '*' },                     { '*', 'a', '*', '*' },                     { '*', '*', '*', 'd' } };     int n = 4;     cout << alphabetWithMaxStars(mat, n);     return 0;}
// Java program to find alphabet in a Matrix// which has maximum number of stars// surrounding itimport java.util.*; class GFG{ // Function to return the count of stars// around a particular indexstatic int countStars(int mat[][], int i, int j, int n){    int count = 0;     int rowNum[] = { -1, -1, -1, 0, 0, 1, 1, 1 };    int colNum[] = { -1, 0, 1, -1, 1, -1, 0, 1 };     // consider all 8 neighbours    for (int k = 0; k < 8; k++)    {        int x = i + rowNum[k];        int y = j + colNum[k];        if (x >= 0 && x < n && y >= 0 && y < n            && mat[x][y] == '*')            count++;    }     return count;} // Function to return the character in a Matrix// which has maximum number of stars around itstatic char alphabetWithMaxStars(int mat[][], int n){    HashMap<Character,Integer> umap =        new HashMap<Character,Integer>();     for (int i = 0; i < n; i++)    {        for (int j = 0; j < n; j++)        {             // If current element is a character            if ((mat[i][j] - 97) >= 0                && (mat[i][j] - 97) < 26)            {                                 // Count of start surrounding it                int stars = countStars(mat, i, j, n);                umap.put((char)mat[i][j], stars);            }        }    }     int max = -1;    char result = 'z' + 1;     // Traverse the map    for (Map.Entry<Character,Integer> x : umap.entrySet())    {        if (x.getValue() > max || (x.getValue() == max            && x.getKey() < result))        {            max = x.getValue();            result = x.getKey();        }    }     return result;} // Driver codepublic static void main(String[] args){    int mat[][] = { { 'b', '*', '*', '*' },                    { '*', '*', 'c', '*' },                    { '*', 'a', '*', '*' },                    { '*', '*', '*', 'd' } };     int n = 4;     System.out.print(alphabetWithMaxStars(mat, n));}} // This code is contributed by PrinciRaj1992
# Python3 program to find alphabet in a# Matrix which has maximum number of stars# surrounding itimport math as mt # Function to return the count of stars# around a particular indexdef countStars(mat, i, j, n):     count = 0     rowNum = [-1, -1, -1, 0, 0, 1, 1, 1 ]    colNum = [-1, 0, 1, -1, 1, -1, 0, 1 ]     # consider all 8 neighbours    for k in range(8):        x = i + rowNum[k]        y = j + colNum[k]        if (x >= 0 and x < n and y >= 0 and            y < n and mat[x][y] == '*'):            count += 1         return count # Function to return the character in a Matrix# which has maximum number of stars around itdef alphabetWithMaxStars(mat, n):     umap = dict()     for i in range(n):        for j in range(n):             # If current element is a character            if ((ord(mat[i][j]) - 97) >= 0 and                (ord(mat[i][j]) - 97) < 26):                # Count of start surrounding it                stars = countStars(mat, i, j, n)                umap[mat[i][j]] = stars                 Max = -1    result = chr(ord('z') + 1)     # Traverse the map    for x in umap:        if (umap[x] > Max or           (umap[x] == Max and x < result)):            Max = umap[x]            result = x             return result # Driver codemat = [[ 'b', '*', '*', '*' ],       [ '*', '*', 'c', '*' ],       [ '*', 'a', '*', '*' ],       [ '*', '*', '*', 'd' ]] n = 4 print(alphabetWithMaxStars(mat, n)) # This code is contributed by# Mohit kumar 29
// C# program to find alphabet in a Matrix// which has maximum number of stars// surrounding itusing System;using System.Collections.Generic; class GFG{ // Function to return the count of stars// around a particular indexstatic int countStars(int [,]mat, int i, int j, int n){    int count = 0;     int []rowNum = { -1, -1, -1, 0, 0, 1, 1, 1 };    int []colNum = { -1, 0, 1, -1, 1, -1, 0, 1 };     // consider all 8 neighbours    for (int k = 0; k < 8; k++)    {        int x = i + rowNum[k];        int y = j + colNum[k];        if (x >= 0 && x < n && y >= 0 && y < n            && mat[x, y] == '*')            count++;    }     return count;} // Function to return the character in a Matrix// which has maximum number of stars around itstatic char alphabetWithMaxStars(int [,]mat, int n){    Dictionary<char,int> umap =        new Dictionary<char,int>();     for (int i = 0; i < n; i++)    {        for (int j = 0; j < n; j++)        {             // If current element is a character            if ((mat[i, j] - 97) >= 0                && (mat[i, j] - 97) < 26)            {                                 // Count of start surrounding it                int stars = countStars(mat, i, j, n);                if(umap.ContainsKey((char)mat[i,j]))                    umap[(char)mat[i,j]] = stars;                else                    umap.Add((char)mat[i,j], stars);            }        }    }     int max = -1;    char result = (char)('z' + 1);     // Traverse the map    foreach(KeyValuePair<char, int> x in umap)    {        if (x.Value > max || (x.Value == max            && x.Key < result))        {            max = x.Value;            result = x.Key;        }    }     return result;} // Driver codepublic static void Main(String[] args){    int [,]mat = { { 'b', '*', '*', '*' },                    { '*', '*', 'c', '*' },                    { '*', 'a', '*', '*' },                    { '*', '*', '*', 'd' } };     int n = 4;     Console.Write(alphabetWithMaxStars(mat, n));}} // This code is contributed by Rajput-Ji
<script>// Javascript program to find alphabet in a Matrix// which has maximum number of stars// surrounding it // Function to return the count of stars// around a particular indexfunction countStars(mat,i,j,n){    let count = 0;         let rowNum = [-1, -1, -1, 0, 0, 1, 1, 1];    let colNum = [-1, 0, 1, -1, 1, -1, 0, 1];         // consider all 8 neighbours    for (let k = 0; k < 8; k++)    {        let x = i + rowNum[k];        let y = j + colNum[k];        if (x >= 0 && x < n && y >= 0 && y < n            && mat[x][y] == '*')            count++;    }      return count;} // Function to return the character in a Matrix// which has maximum number of stars around itfunction alphabetWithMaxStars(mat,n){    let umap = new Map();      for (let i = 0; i < n; i++)    {        for (let j = 0; j < n; j++)        {              // If current element is a character            if ((mat[i][j].charCodeAt(0) - 97) >= 0                && (mat[i][j].charCodeAt(0) - 97) < 26)            {                                  // Count of start surrounding it                let stars = countStars(mat, i, j, n);                umap.set((mat[i][j]), stars);            }        }    }      let max = -1;    let result = String.fromCharCode('z'.charCodeAt(0) + 1);      // Traverse the map    for (let [key, value] of umap.entries())    {        if (value > max || (value == max            && key < result))        {            max = value;            result = key;        }    }      return result;} // Driver codelet mat = [[ 'b', '*', '*', '*' ],       [ '*', '*', 'c', '*' ],       [ '*', 'a', '*', '*' ],       [ '*', '*', '*', 'd' ]];        let n = 4;document.write(alphabetWithMaxStars(mat, n));     // This code is contributed by unknown2108.</script>
a
 
Another approach:  
C++
Java
Python3
C#
Javascript
// C++ program to find alphabet in a Matrix// which has maximum number of stars// surrounding it#include <bits/stdc++.h>using namespace std; /**    * Counts the number of stars around the letter at position i,j    * start at position max(i-1,0),max(j-1,0) and iterate the 3*3 mini matrix    * while watching out the boundaries of    * our main matrix.     * @param i    * @param j    * @param mat    * @return    */int countStars(int i, int j, vector<vector<char>> mat){    int initialRow = i != 0 ? i - 1 : i;    int initialCol = j != 0 ? j - 1 : j;    int stars = 0;    for (int row=initialRow;(row <= i + 1) &&         row < mat.size() ; row++)    {        for (int col=initialCol;(col <= j + 1) &&             col < mat.size() ; col++)        {            if (mat[row][col] == '*')            {                stars++;            }        }    }    return stars;} // Function to return the character in a Matrix// which has maximum number of stars around itchar getStarredLetter (vector<vector<char>> mat){    char currentSuperStar = 'a';    int currentFans = 0;    for (int i = 0 ; i < mat.size() ; i++)    {        vector<char> row = mat[i];        for (int j = 0 ; j < row.size(); j++)        {            char currentChar = row[j];            if (currentChar != '*')            {                // Count of start surrounding it                int fans = countStars(i, j, mat);                if (fans > currentFans)                {                    currentSuperStar = currentChar;                    currentFans = fans;                }                else if(fans == currentFans &&                        currentChar < currentSuperStar)                {                    currentSuperStar = currentChar;                }            }        }    }    return currentSuperStar;} // Driver Codeint main(){    vector<vector<char>> mat = { { 'b', '*', '*', '*' },                                { '*', '*', 'c', '*' },                                { '*', 'a', '*', '*' },                                { '*', '*', '*', 'd' } };    cout << getStarredLetter(mat);    return 0;} // This code is contributed by rag2127.
// Java program to find alphabet in a Matrix// which has maximum number of stars// surrounding itpublic class SuperStarLetter {         // Function to return the character in a Matrix    // which has maximum number of stars around it    private static char getStarredLetter (char[][] mat) {        char currentSuperStar = 'a';        int currentFans = 0;        for (int i=0 ; i < mat.length ; i++) {            char[] row = mat[i];            for (int j = 0 ; j < row.length; j++) {                char currentChar = row[j];                if (currentChar != '*') {                                         // Count of start surrounding it                    int fans = countStars(i, j, mat);                    if (fans > currentFans) {                        currentSuperStar = currentChar;                        currentFans = fans;                    } else if (fans == currentFans &&                            currentChar < currentSuperStar) {                        currentSuperStar = currentChar;                    }                }            }        }        return currentSuperStar;    }     /**    * Counts the number of stars around the letter at position i,j    * start at position max(i-1,0),max(j-1,0) and iterate the 3*3 mini matrix    * while watching out the boundaries of    * our main matrix.    * @param i    * @param j    * @param mat    * @return    */    private static int countStars(int i, int j, char[][] mat) {        int initialRow = i != 0 ? i-1 : i;        int initialCol = j != 0 ? j-1 : j;        int stars= 0;        for (int row=initialRow;(row <= i+1) && row < mat.length ; row++) {            for (int col=initialCol;(col <= j+1) && col < mat.length ; col++) {                if (mat[row][col] == '*') {                    stars++;                }            }        }        return stars;    }        //Driver Code    public static void main(String[] args) {        char[][] mat = { { 'b', '*', '*', '*' },                     { '*', '*', 'c', '*' },                     { '*', 'a', '*', '*' },                     { '*', '*', '*', 'd' } };        System.out.println(getStarredLetter(mat));             } }
# Python3 program to find alphabet# in a Matrix which has maximum# number of stars surrounding it # Function to return the character# in a Matrix which has maximum# number of stars around itdef getStarredLetter (mat) :    currentSuperStar = 'a'    currentFans = 0    for i in range(len(mat)) :        row = mat[i]                 for j in range(len(row)) :                         currentChar = row[j]            if (currentChar != '*') :                                     # Count of start surrounding it                fans = countStars(i, j, mat)                if (fans > currentFans) :                    currentSuperStar = currentChar                    currentFans = fans                                 elif (fans == currentFans and                      currentChar < currentSuperStar) :                    currentSuperStar = currentChar;                         return currentSuperStar;     """    * Counts the number of stars around the    * letter at position i,j start at position    * max(i-1,0),max(j-1,0) and iterate the 3*3    * mini matrix while watching out the boundaries    * of our main matrix.    * @param i    * @param j    * @param mat    * @return"""def countStars(i, j, mat) :         if i != 0 :        initialRow = i - 1    else :        initialRow = i                  if j != 0 :        initialCol = j - 1    else :        initialCol = j             stars = 0         row = initialRow         while ((row <= i + 1) and (row < len(mat))):        col = initialCol        while ((col <= j + 1) and (col < len(mat))):            if (mat[row][col] == '*') :                                 stars += 1                         col += 1                     row += 1             return stars     # Driver Codeif __name__ == "__main__" :         mat = [ [ 'b', '*', '*', '*' ],            [ '*', '*', 'c', '*' ],            [ '*', 'a', '*', '*' ],            [ '*', '*', '*', 'd' ] ]                 print(getStarredLetter(mat))         # This code is contributed by Ryugaa
// C# program to find row with// max sum in a matrixusing System; public class SuperStarLetter{         // Function to return the character in a Matrix    // which has maximum number of stars around it    private static char getStarredLetter (char[,] mat)    {        char currentSuperStar = 'a';        int currentFans = 0;        for (int i = 0 ; i < mat.GetLength(0) ; i++)        {            char[] row = GetRow(mat, i);            for (int j = 0 ; j < row.Length; j++)            {                char currentChar = row[j];                if (currentChar != '*')                {                                         // Count of start surrounding it                    int fans = countStars(i, j, mat);                    if (fans > currentFans)                    {                        currentSuperStar = currentChar;                        currentFans = fans;                    }                    else if (fans == currentFans &&                            currentChar < currentSuperStar)                    {                        currentSuperStar = currentChar;                    }                }            }        }        return currentSuperStar;    }     public static char[] GetRow(char[,] matrix, int row){    var rowLength = matrix.GetLength(1);    var rowVector = new char[rowLength];     for (var i = 0; i < rowLength; i++)    rowVector[i] = matrix[row, i];     return rowVector;}    /**    * Counts the number of stars around the letter at position i,j    * start at position max(i-1,0),max(j-1,0) and iterate the 3*3 mini matrix    * while watching out the boundaries of    * our main matrix.    * @param i    * @param j    * @param mat    * @return    */    private static int countStars(int i, int j, char[,] mat)    {        int initialRow = i != 0 ? i-1 : i;        int initialCol = j != 0 ? j-1 : j;        int stars= 0;        for (int row = initialRow;(row <= i+1) && row < mat.GetLength(0) ; row++)        {            for (int col=initialCol;(col <= j+1) && col < mat.GetLength(1); col++)            {                if (mat[row,col] == '*')                {                    stars++;                }            }        }        return stars;    }         // Driver Code    public static void Main(String[] args)    {        char[,] mat = { { 'b', '*', '*', '*' },                    { '*', '*', 'c', '*' },                    { '*', 'a', '*', '*' },                    { '*', '*', '*', 'd' } };        Console.WriteLine(getStarredLetter(mat));             }} // This code has been contributed by 29AjayKumar
<script>// Javascript program to find alphabet in a Matrix// which has maximum number of stars// surrounding it // Function to return the character in a Matrix    // which has maximum number of stars around itfunction getStarredLetter (mat){    let currentSuperStar = 'a';        let currentFans = 0;        for (let i = 0 ; i < mat.length ; i++)        {            let row = mat[i];            for (let j = 0 ; j < row.length; j++)            {                let currentChar = row[j];                if (currentChar != '*')                {                                          // Count of start surrounding it                    let fans = countStars(i, j, mat);                    if (fans > currentFans)                    {                        currentSuperStar = currentChar;                        currentFans = fans;                    }                    else if (fans == currentFans &&                            currentChar < currentSuperStar)                    {                        currentSuperStar = currentChar;                    }                }            }        }        return currentSuperStar;} /**    * Counts the number of stars around the letter at position i,j    * start at position max(i-1,0),max(j-1,0) and iterate the 3*3 mini matrix    * while watching out the boundaries of    * our main matrix.    * @param i    * @param j    * @param mat    * @return    */function countStars(i,j,mat){    let initialRow = i != 0 ? i-1 : i;        let initialCol = j != 0 ? j-1 : j;        let stars= 0;        for (let row=initialRow;(row <= i+1) && row < mat.length ; row++) {            for (let col=initialCol;(col <= j+1) && col < mat.length ; col++) {                if (mat[row][col] == '*') {                    stars++;                }            }        }        return stars;}  // Driver Codelet mat = [[ 'b', '*', '*', '*' ],                     [ '*', '*', 'c', '*' ],                     [ '*', 'a', '*', '*' ],                     [ '*', '*', '*', 'd' ] ];                      document.write(getStarredLetter(mat)); // This code is contributed by patel2127</script>
a
 
Time Complexity: O(N * M) Auxiliary Space: O(N * M) 
prmdk
ankthon
mohit kumar 29
29AjayKumar
princiraj1992
Rajput-Ji
rag2127
unknown2108
patel2127
pankajsharmagfg
cpp-unordered_map
D-E-Shaw
frequency-counting
Algorithms
Matrix
D-E-Shaw
Matrix
Algorithms
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