算法设计：如何解决布尔矩阵问题？？

2021年3月22日15:33:53 发表评论 760 次浏览

本文概述

给定大小为M X N的布尔矩阵mat [M] [N], 对其进行修改, 使得如果矩阵单元mat [i] [j]为1(或true), 则将第i行和第j列的所有单元格都设置为1。

Example 1
The matrix
1 0
0 0
should be changed to following
1 1
1 0

Example 2
The matrix
0 0 0
0 0 1
should be changed to following
0 0 1
1 1 1

Example 3
The matrix
1 0 0 1
0 0 1 0
0 0 0 0
should be changed to following
1 1 1 1
1 1 1 1
1 0 1 1

推荐：请在"实践首先, 在继续解决方案之前。

方法1(使用两个临时数组)

1)创建两个临时数组row [M]和col [N]。将row []和col []的所有值初始化为0。

2)遍历输入矩阵mat [M] [N]。如果看到输入mat [i] [j]为true, 则将row [i]和col [j]标记为true。

3)再次遍历输入矩阵mat [M] [N]。对于每个入口mat [i] [j], 检查row [i]和col [j]的值。如果两个值(row [i]或col [j])中的任何一个为true, 则将mat [i] [j]标记为true。

感谢Dixit Sethi建议这种方法。

C ++

// C++ Code For A Boolean Matrix Question
#include <bits/stdc++.h>
  
using namespace std;
#define R 3
#define C 4
  
void modifyMatrix( bool mat[R][C])
{
     bool row[R];
     bool col[C];
  
     int i, j;
      
     /* Initialize all values of row[] as 0 */
     for (i = 0; i < R; i++)
     {
     row[i] = 0;
     }
  
     /* Initialize all values of col[] as 0 */
     for (i = 0; i < C; i++)
     {
     col[i] = 0;
     }
  
     // Store the rows and columns to be marked as
     // 1 in row[] and col[] arrays respectively
     for (i = 0; i < R; i++)
     {
         for (j = 0; j < C; j++)
         {
             if (mat[i][j] == 1)
             {
                 row[i] = 1;
                 col[j] = 1;
             }
         }
     }
  
     // Modify the input matrix mat[] using the 
     // above constructed row[] and col[] arrays
     for (i = 0; i < R; i++)
     {
         for (j = 0; j < C; j++)
         {
             if ( row[i] == 1 || col[j] == 1 )
             {
                 mat[i][j] = 1;
             }
         }
     }
}
  
/* A utility function to print a 2D matrix */
void printMatrix( bool mat[R][C])
{
     int i, j;
     for (i = 0; i < R; i++)
     {
         for (j = 0; j < C; j++)
         {
             cout << mat[i][j];
         }
         cout << endl;
     }
}
  
// Driver Code
int main()
{
     bool mat[R][C] = { {1, 0, 0, 1}, {0, 0, 1, 0}, {0, 0, 0, 0}};
  
     cout << "Input Matrix \n" ;
     printMatrix(mat);
  
     modifyMatrix(mat);
  
     printf ( "Matrix after modification \n" );
     printMatrix(mat);
  
     return 0;
}
  
// This code is contributed 
// by Akanksha Rai(Abby_akku)

Java

// Java Code For A Boolean Matrix Question
class GFG
{
     public static void modifyMatrix( int mat[ ][ ], int R, int C)
     {
         int row[ ]= new int [R];
         int col[ ]= new int [C];
         int i, j;
      
         /* Initialize all values of row[] as 0 */
         for (i = 0 ; i < R; i++)
         {
         row[i] = 0 ;
         }
      
      
         /* Initialize all values of col[] as 0 */
         for (i = 0 ; i < C; i++)
         {
         col[i] = 0 ;
         }
      
      
         /* Store the rows and columns to be marked as
         1 in row[] and col[] arrays respectively */
         for (i = 0 ; i < R; i++)
         {
             for (j = 0 ; j < C; j++)
             {
                 if (mat[i][j] == 1 )
                 {
                     row[i] = 1 ;
                     col[j] = 1 ;
                 }
             }
         }
      
         /* Modify the input matrix mat[] using the
         above constructed row[] and col[] arrays */
         for (i = 0 ; i < R; i++)
         {
             for (j = 0 ; j < C; j++)
             {
                 if ( row[i] == 1 || col[j] == 1 )
                 {
                     mat[i][j] = 1 ;
                 }
             }
         }
     }
      
     /* A utility function to print a 2D matrix */
     public static void printMatrix( int mat[ ][ ], int R, int C)
     {
         int i, j;
         for (i = 0 ; i < R; i++)
         {
             for (j = 0 ; j < C; j++)
             {
                 System.out.print(mat[i][j]+ " " );
             }
             System.out.println();
         }
     }
      
     /* Driver program to test above functions */
     public static void main(String[] args) 
     {
         int mat[ ][ ] = { { 1 , 0 , 0 , 1 }, { 0 , 0 , 1 , 0 }, { 0 , 0 , 0 , 0 }, };
                      
                 System.out.println( "Matrix Intially" );
                  
                 printMatrix(mat, 3 , 4 );
              
                 modifyMatrix(mat, 3 , 4 );
                 System.out.println( "Matrix after modification n" );
                 printMatrix(mat, 3 , 4 );
              
     } 
  
}
  
// This code is contributed by Kamal Rawal

Python3

# Python3 Code For A Boolean Matrix Question
R = 3
C = 4
  
def modifyMatrix(mat):
     row = [ 0 ] * R 
     col = [ 0 ] * C 
      
     # Initialize all values of row[] as 0 
     for i in range ( 0 , R):
         row[i] = 0
          
     # Initialize all values of col[] as 0 
     for i in range ( 0 , C) :
         col[i] = 0
  
  
     # Store the rows and columns to be marked 
     # as 1 in row[] and col[] arrays respectively 
     for i in range ( 0 , R) :
          
         for j in range ( 0 , C) :
             if (mat[i][j] = = 1 ) :
                 row[i] = 1
                 col[j] = 1
              
     # Modify the input matrix mat[] using the 
     # above constructed row[] and col[] arrays 
     for i in range ( 0 , R) :
          
         for j in range ( 0 , C):
             if ( row[i] = = 1 or col[j] = = 1 ) :
                 mat[i][j] = 1
                  
# A utility function to print a 2D matrix 
def printMatrix(mat) :
     for i in range ( 0 , R):
          
         for j in range ( 0 , C) :
             print (mat[i][j], end = " " )
         print ()
          
# Driver Code
mat = [ [ 1 , 0 , 0 , 1 ], [ 0 , 0 , 1 , 0 ], [ 0 , 0 , 0 , 0 ] ] 
  
print ( "Input Matrix n" )
printMatrix(mat)
  
modifyMatrix(mat)
  
print ( "Matrix after modification n" )
printMatrix(mat)
  
# This code is contributed by Nikita Tiwari.

C#

// C# Code For A Boolean
// Matrix Question
using System;
  
class GFG
{
     public static void modifyMatrix( int [, ]mat, int R, int C)
     {
         int []row = new int [R];
         int []col = new int [C];
         int i, j;
      
         /* Initialize all values
         of row[] as 0 */
         for (i = 0; i < R; i++)
         {
         row[i] = 0;
         }
      
      
         /* Initialize all values
         of col[] as 0 */
         for (i = 0; i < C; i++)
         {
         col[i] = 0;
         }
      
      
         /* Store the rows and columns 
         to be marked as 1 in row[] 
         and col[] arrays respectively */
         for (i = 0; i < R; i++)
         {
             for (j = 0; j < C; j++)
             {
                 if (mat[i, j] == 1)
                 {
                     row[i] = 1;
                     col[j] = 1;
                 }
             }
         }
      
         /* Modify the input matrix 
         mat[] using the above 
         constructed row[] and 
         col[] arrays */
         for (i = 0; i < R; i++)
         {
             for (j = 0; j < C; j++)
             {
                 if (row[i] == 1 || col[j] == 1)
                 {
                     mat[i, j] = 1;
                 }
             }
         }
     }
      
     /* A utility function to
     print a 2D matrix */
     public static void printMatrix( int [, ]mat, int R, int C)
     {
         int i, j;
         for (i = 0; i < R; i++)
         {
             for (j = 0; j < C; j++)
             {
                 Console.Write(mat[i, j] + " " );
             }
             Console.WriteLine();
         }
     }
      
     // Driver code
     static public void Main ()
     {
         int [, ]mat = {{1, 0, 0, 1}, {0, 0, 1, 0}, {0, 0, 0, 0}};
              
         Console.WriteLine( "Matrix Intially" );
          
         printMatrix(mat, 3, 4);
      
         modifyMatrix(mat, 3, 4);
         Console.WriteLine( "Matrix after " +
                         "modification n" );
         printMatrix(mat, 3, 4);
          
     }
}
  
// This code is contributed by ajit

的PHP

<?php 
// PHP Code For A Boolean
// Matrix Question
$R = 3;
$C = 4;
  
function modifyMatrix(& $mat )
{
     global $R , $C ;
     $row = array ();
     $col = array ();
  
     /* Initialize all values 
        of row[] as 0 */
     for ( $i = 0; $i < $R ; $i ++)
     {
         $row [ $i ] = 0;
     }
  
  
     /* Initialize all values 
        of col[] as 0 */
     for ( $i = 0; $i < $C ; $i ++)
     {
         $col [ $i ] = 0;
     }
  
  
     /* Store the rows and columns 
        to be marked as 1 in row[] 
        and col[] arrays respectively */
     for ( $i = 0; $i < $R ; $i ++)
     {
         for ( $j = 0; $j < $C ; $j ++)
         {
             if ( $mat [ $i ][ $j ] == 1)
             {
                 $row [ $i ] = 1;
                 $col [ $j ] = 1;
             }
         }
     }
  
     /* Modify the input matrix mat[]
        using the above constructed 
        row[] and col[] arrays */
     for ( $i = 0; $i < $R ; $i ++)
     {
         for ( $j = 0; $j < $C ; $j ++)
         {
             if ( $row [ $i ] == 1 || 
                 $col [ $j ] == 1 )
             {
                 $mat [ $i ][ $j ] = 1;
             }
         }
     }
}
  
/* A utility function to
    print a 2D matrix */
function printMatrix(& $mat )
{
     global $R , $C ;
     for ( $i = 0; $i < $R ; $i ++)
     {
         for ( $j = 0; $j < $C ; $j ++)
         {
             echo $mat [ $i ][ $j ] . " " ;
         }
         echo "\n" ;
     }
}
  
// Driver code 
$mat = array ( array (1, 0, 0, 1), array (0, 0, 1, 0), array (0, 0, 0, 0));
  
echo "Input Matrix \n" ;
printMatrix( $mat );
  
modifyMatrix( $mat );
  
echo "Matrix after modification \n" ;
printMatrix( $mat );
  
// This code is contributed 
// by ChitraNayal
?>

输出如下：

Input Matrix
1 0 0 1
0 0 1 0
0 0 0 0
Matrix after modification
1 1 1 1
1 1 1 1
1 0 1 1

时间复杂度：

O(M * N)

辅助空间：

O(M + N)

方法2(方法1的空间优化版本)

该方法是上述方法1的空间优化版本。该方法使用输入矩阵的第一行和第一列代替方法1的辅助数组row []和col []。因此, 我们要做的是：首先注意第一行和第一列, 并将这两个信息存储在两个标志变量rowFlag和colFlag中。获得此信息后, 我们可以将第一行和第一列用作辅助数组, 并将方法1应用于大小为(M-1)*(N-1)的子矩阵(不包括第一行和第一列的矩阵)。

1)扫描第一行并设置一个变量rowFlag以指示是否需要在第一行中设置全1。

2)扫描第一列并设置变量colFlag以指示是否需要在第一列中设置全1。

3)分别使用第一行和第一列作为辅助数组row []和col [], 将矩阵视为从第二行和第二列开始的子矩阵, 并应用方法1。

4)最后, 如果需要, 使用rowFlag和colFlag更新第一行和第一列。

时间复杂度：O(M * N)

辅助空间：O(1)

感谢Sidh提出了这种方法。

C ++

#include <bits/stdc++.h>
using namespace std;
#define R 3
#define C 4
  
void modifyMatrix( int mat[R][C])
{
     // variables to check if there are any 1
     // in first row and column
     bool row_flag = false ;
     bool col_flag = false ;
  
     // updating the first row and col if 1
     // is encountered
     for ( int i = 0; i < R; i++) {
         for ( int j = 0; j < C; j++) {
             if (i == 0 && mat[i][j] == 1)
                 row_flag = true ;
  
             if (j == 0 && mat[i][j] == 1)
                 col_flag = true ;
  
             if (mat[i][j] == 1) {
  
                 mat[0][j] = 1;
                 mat[i][0] = 1;
             }
         }
     }
  
     // Modify the input matrix mat[] using the
     // first row and first column of Matrix mat
     for ( int i = 1; i < R; i++) {
         for ( int j = 1; j < C; j++) {
  
             if (mat[0][j] == 1 || mat[i][0] == 1) {
                 mat[i][j] = 1;
             }
         }
     }
  
     // modify first row if there was any 1
     if (row_flag == true ) {
         for ( int i = 0; i < C; i++) {
             mat[0][i] = 1;
         }
     }
  
     // modify first col if there was any 1
     if (col_flag == true ) {
         for ( int i = 0; i < R; i++) {
             mat[i][0] = 1;
         }
     }
}
  
/* A utility function to print a 2D matrix */
void printMatrix( int mat[R][C])
{
     for ( int i = 0; i < R; i++) {
         for ( int j = 0; j < C; j++) {
             cout << mat[i][j];
         }
         cout << "\n" ;
     }
}
  
// Driver function to test the above function
int main()
{
  
     int mat[R][C] = { { 1, 0, 0, 1 }, { 0, 0, 1, 0 }, { 0, 0, 0, 0 } };
  
     cout << "Input Matrix :\n" ;
     printMatrix(mat);
  
     modifyMatrix(mat);
  
     cout << "Matrix After Modification :\n" ;
     printMatrix(mat);
     return 0;
}
  
// This code is contributed by Nikita Tiwari

Java

class GFG
{ 
     public static void modifyMatrix( int mat[][]){
                  
         // variables to check if there are any 1 
         // in first row and column
         boolean row_flag = false ;
         boolean col_flag = false ;
                  
         // updating the first row and col if 1
         // is encountered
         for ( int i = 0 ; i < mat.length; i++ ){
                 for ( int j = 0 ; j < mat[ 0 ].length; j++){
                         if (i == 0 && mat[i][j] == 1 )
                             row_flag = true ;
                          
                         if (j == 0 && mat[i][j] == 1 )
                             col_flag = true ;
                          
                         if (mat[i][j] == 1 ){
                              
                             mat[ 0 ][j] = 1 ;
                             mat[i][ 0 ] = 1 ;
                         }
                          
                     }
                 }
                  
         // Modify the input matrix mat[] using the 
         // first row and first column of Matrix mat
         for ( int i = 1 ; i < mat.length; i ++){
                 for ( int j = 1 ; j < mat[ 0 ].length; j ++){
                          
                     if (mat[ 0 ][j] == 1 || mat[i][ 0 ] == 1 ){
                             mat[i][j] = 1 ;
                         }
                     }
                 }
                  
         // modify first row if there was any 1
         if (row_flag == true ){
             for ( int i = 0 ; i < mat[ 0 ].length; i++){
                         mat[ 0 ][i] = 1 ;
                     }
                 }
                  
         // modify first col if there was any 1
         if (col_flag == true ){
             for ( int i = 0 ; i < mat.length; i ++){
                         mat[i][ 0 ] = 1 ;
             }
         }
     }
              
     /* A utility function to print a 2D matrix */
     public static void printMatrix( int mat[][]){
         for ( int i = 0 ; i < mat.length; i ++){
             for ( int j = 0 ; j < mat[ 0 ].length; j ++){
                 System.out.print( mat[i][j] );
             }
                 System.out.println( "" );
         }
     }
              
     // Driver function to test the above function
     public static void main(String args[] ){
                  
         int mat[][] = {{ 1 , 0 , 0 , 1 }, { 0 , 0 , 1 , 0 }, { 0 , 0 , 0 , 0 }};
                  
         System.out.println( "Input Matrix :" );
         printMatrix(mat);
              
         modifyMatrix(mat);
              
         System.out.println( "Matrix After Modification :" );
         printMatrix(mat);
              
     }
}
  
// This code is contributed by Arnav Kr. Mandal.

Python3

# Python3 Code For A Boolean Matrix Question
def modifyMatrix(mat) :
      
     # variables to check if there are any 1 
     # in first row and column
     row_flag = False
     col_flag = False
              
     # updating the first row and col 
     # if 1 is encountered
     for i in range ( 0 , len (mat)) :
          
         for j in range ( 0 , len (mat)) :
             if (i = = 0 and mat[i][j] = = 1 ) :
                 row_flag = True
                      
             if (j = = 0 and mat[i][j] = = 1 ) :
                 col_flag = True
              
             if (mat[i][j] = = 1 ) :
                 mat[ 0 ][j] = 1
                 mat[i][ 0 ] = 1
                  
     # Modify the input matrix mat[] using the 
     # first row and first column of Matrix mat
     for i in range ( 1 , len (mat)) :
          
         for j in range ( 1 , len (mat) + 1 ) :
             if (mat[ 0 ][j] = = 1 or mat[i][ 0 ] = = 1 ) :
                 mat[i][j] = 1
                  
     # modify first row if there was any 1
     if (row_flag = = True ) :
         for i in range ( 0 , len (mat)) :
             mat[ 0 ][i] = 1
              
     # modify first col if there was any 1
     if (col_flag = = True ) :
         for i in range ( 0 , len (mat)) :
             mat[i][ 0 ] = 1
              
# A utility function to print a 2D matrix
def printMatrix(mat) :
      
     for i in range ( 0 , len (mat)) :
         for j in range ( 0 , len (mat) + 1 ) :
             print ( mat[i][j], end = "" )
          
         print ()
          
# Driver Code
mat = [ [ 1 , 0 , 0 , 1 ], [ 0 , 0 , 1 , 0 ], [ 0 , 0 , 0 , 0 ] ]
          
print ( "Input Matrix :" )
printMatrix(mat)
      
modifyMatrix(mat)
      
print ( "Matrix After Modification :" )
printMatrix(mat)
  
# This code is contributed by Nikita tiwari.

C#

// C# Code For A Boolean
// Matrix Question
using System;
  
class GFG
{ 
     public static void modifyMatrix( int [, ] mat)
     {
                  
         // variables to check 
         // if there are any 1 
         // in first row and column
         bool row_flag = false ;
         bool col_flag = false ;
                  
         // updating the first
         // row and col if 1
         // is encountered
         for ( int i = 0;
                  i < mat.GetLength(0); i++ )
         {
                 for ( int j = 0; 
                          j < mat.GetLength(1); j++)
                 {
                         if (i == 0 && mat[i, j] == 1)
                             row_flag = true ;
                          
                         if (j == 0 && mat[i, j] == 1)
                             col_flag = true ;
                          
                         if (mat[i, j] == 1)
                         {
                             mat[0, j] = 1;
                             mat[i, 0] = 1;
                         }
                          
                     }
                 }
                  
         // Modify the input matrix mat[] 
         // using the first row and first
         // column of Matrix mat
         for ( int i = 1; 
                  i < mat.GetLength(0); i ++)
         {
                 for ( int j = 1; 
                          j < mat.GetLength(1); j ++)
                 {
                          
                     if (mat[0, j] == 1 || 
                         mat[i, 0] == 1)
                     {
                             mat[i, j] = 1;
                         }
                     }
                 }
                  
         // modify first row
         // if there was any 1
         if (row_flag == true )
         {
             for ( int i = 0; 
                      i < mat.GetLength(1); i++)
             {
                         mat[0, i] = 1;
             }
         }
                  
         // modify first col if
         // there was any 1
         if (col_flag == true )
         {
             for ( int i = 0; 
                      i < mat.GetLength(0); i ++)
             {
                         mat[i, 0] = 1;
             }
         }
     }
              
     /* A utility function 
     to print a 2D matrix */
     public static void printMatrix( int [, ] mat)
     {
         for ( int i = 0; 
                  i < mat.GetLength(0); i ++)
         {
             for ( int j = 0; 
                      j < mat.GetLength(1); j ++)
             {
                 Console.Write(mat[i, j] + " " );
             }
                 Console.Write( "\n" );
         }
     }
              
     // Driver Code
     public static void Main()
     {
         int [, ] mat = {{1, 0, 0, 1}, {0, 0, 1, 0}, {0, 0, 0, 0}};
                  
         Console.Write( "Input Matrix :\n" );
         printMatrix(mat);
              
         modifyMatrix(mat);
              
         Console.Write( "Matrix After " + 
                       "Modification :\n" );
         printMatrix(mat);
     }
}
  
// This code is contributed
// by ChitraNayal

的PHP

<?php 
// PHP Code For A Boolean
// Matrix Question
$R = 3;
$C = 4;
  
function modifyMatrix(& $mat )
{
     global $R , $C ;
      
     // variables to check if 
     // there are any 1 in 
     // first row and column
     $row_flag = false;
     $col_flag = false;
  
     // updating the first 
     // row and col if 1
     // is encountered
     for ( $i = 0; $i < $R ; $i ++) 
     {
         for ( $j = 0; $j < $C ; $j ++) 
         {
             if ( $i == 0 && $mat [ $i ][ $j ] == 1)
                 $row_flag = true;
  
             if ( $j == 0 && $mat [ $i ][ $j ] == 1)
                 $col_flag = true;
  
             if ( $mat [ $i ][ $j ] == 1) 
             {
                 $mat [0][ $j ] = 1;
                 $mat [ $i ][0] = 1;
             }
         }
     }
  
     // Modify the input matrix 
     // mat[] using the first 
     // row and first column of 
     // Matrix mat
     for ( $i = 1; $i < $R ; $i ++) 
     {
         for ( $j = 1; $j < $C ; $j ++)
         {
             if ( $mat [0][ $j ] == 1 || 
                 $mat [ $i ][0] == 1)
             {
                 $mat [ $i ][ $j ] = 1;
             }
         }
     }
  
     // modify first row 
     // if there was any 1
     if ( $row_flag == true) 
     {
         for ( $i = 0; $i < $C ; $i ++)
         {
             $mat [0][ $i ] = 1;
         }
     }
  
     // modify first col 
     // if there was any 1
     if ( $col_flag == true) 
     {
         for ( $i = 0; $i < $R ; $i ++)
         {
             $mat [ $i ][0] = 1;
         }
     }
}
  
/* A utility function
to print a 2D matrix */
function printMatrix(& $mat )
{
     global $R , $C ;
     for ( $i = 0; $i < $R ; $i ++) 
     {
         for ( $j = 0; $j < $C ; $j ++)
         {
             echo $mat [ $i ][ $j ]. " " ;
         }
         echo "\n" ;
     }
}
  
// Driver Code
$mat = array ( array (1, 0, 0, 1 ), array (0, 0, 1, 0 ), array (0, 0, 0, 0 ));
  
echo "Input Matrix :\n" ;
printMatrix( $mat );
  
modifyMatrix( $mat );
  
echo "Matrix After Modification :\n" ;
printMatrix( $mat );
  
// This code is conrtributed 
// by ChitraNayal
?>

输出如下：

Input Matrix :
1001
0010
0000
Matrix After Modification :
1111
1111
1011
木子山

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