[英]How to delete column in 2d array c++ with dynamic array?
我想在二维数组中删除最大 integer 的列,我是这样做的,但是为什么要删除列和行呢? 我可以解决这个问题并只删除列吗? 任务是用删除命令完成的,但现在我认为这是不可能的
#include <iostream>
using namespace std;
int main()
{
int row = 3, col = 3;
int** arr = new int* [row];
for(int i = 0; i < row; i++){
arr[i] = new int[col];
}
for(int i = 0; i < row; i++){
for(int j = 0; j < col; j++) {
cin >> arr[i][j];
}
}
for(int i = 0; i < row; i++){
for(int j = 0; j < col; j++) {
cout << arr[i][j] << " ";
}
cout << endl;
}
cout << " ------------- " << endl;
int max = 0, index = 0;
for(int i =0; i < row; i++){
for(int j = 0; j < col; j++){
if(arr[i][j] > max){
max = arr[i][j];
index = i;
}
}
}
delete [] arr[index];
int** tmp = new int*[index - 1];
int tmpI = 0;
for(int i = 0; i < col; i++){
if(i != index){
tmp[tmpI++] = arr[i];
}
}
delete [] arr;
arr = tmp;
col = col - 1;
for(int i = 0; i < row; i++){
for(int j = 0; j < col; j++) {
cout << arr[i][j] << " ";
}
cout << endl;
}
}
对于初学者,变量索引设置为行号
index = i;
然后这一行被删除
delete [] arr[index];
但是您将删除一列而不是一行。 所以这段代码没有意义。
此外,您正在错误地搜索最大元素。 如果用户将输入所有负值,则最大值将等于 0,尽管数组中不存在具有该值的元素。
在这份声明中
int** tmp = new int*[index - 1];
您分配了一个数组,其行数比原始数组中的行数少一。 此外,如果索引等于 0,则分配了很大范围的 memory。
这个说法
delete [] arr;
产生 memory 泄漏。
看来您需要的是以下内容
#include <iostream>
int main()
{
size_t row = 3, col = 3;
int **arr = new int * [row];
for ( size_t i = 0; i < row; i++ )
{
arr[i] = new int[col];
}
for ( size_t i = 0; i < row; i++ )
{
for ( size_t j = 0; j < col; j++ )
{
std::cin >> arr[i][j];
}
}
for ( size_t i = 0; i < row; i++ )
{
for ( size_t j = 0; j < col; j++ )
{
std::cout << arr[i][j] << " ";
}
std::cout << std::endl;
}
std::cout << "------------- " << std::endl;
size_t max_i = 0, max_j = 0;
for ( size_t i = 0; i < row; i++ )
{
for ( size_t j = 0; j < col; j++ )
{
if ( arr[max_i][max_j] < arr[i][j] )
{
max_i = i; max_j = j;
}
}
}
int **tmp = new int*[row];
for ( size_t i = 0; i < row; i++ )
{
tmp[i] = new int[col-1];
}
for ( size_t i = 0; i < row; i++ )
{
for ( size_t j = 0, k = 0; j < col; j++ )
{
if ( j != max_j ) tmp[i][k++] = arr[i][j];
}
}
for ( size_t i = 0; i < row; i++ )
{
delete [] arr[i];
}
delete [] arr;
arr = tmp;
--col;
for ( size_t i = 0; i < row; i++ )
{
for ( size_t j = 0; j < col; j++ )
{
std::cout << arr[i][j] << " ";
}
std::cout << std::endl;
}
for ( size_t i = 0; i < row; i++ )
{
delete [] arr[i];
}
delete [] arr;
return 0;
}
程序 output 可能看起来像
1 2 3
6 5 4
7 9 8
-------------
1 3
6 4
7 8
这是一个替代建议:您以row x column
格式存储数据。 如果您更改为column x row
格式,则删除一列会变得更容易。 我还制作了一个助手 function 来打印矩阵,并将输入循环和找到最大值的循环结合起来。
#include <iostream>
#include <iomanip>
#include <cstdlib> // for rand
#include <climits>
using namespace std;
void print_matrix(int** arr, int rows, int columns)
{
for(int row = 0; row < rows; row++){
for(int col = 0; col < columns; col++) {
cout << setw(2) << arr[col][row] << " ";
}
cout << "\n";
}
}
int main()
{
srand(time(nullptr)); // For testing
int rows = 3, columns = 3;
// Create the matrix
int** arr = new int *[columns];
for (int col = 0; col < columns; col++) {
arr[col] = new int[rows];
}
// Input values - finding max, too
int max_value = INT_MIN, max_value_column = -1;
for (int row = 0; row < rows; row++) {
for (int col = 0; col < columns; col++) {
//cin >> arr[col][row];
arr[col][row] = rand() % 50; // Using rand for testing.
if (arr[col][row] > max_value) {
max_value = arr[col][row];
max_value_column = col;
}
}
}
print_matrix(arr, rows, columns);
cout << " ------------- " << endl;
// Delete the column with max
delete [] arr[max_value_column];
columns--;
// Shift columns to the right of the deleted column left one
for (int col = max_value_column; col < columns; col++) {
arr[col] = arr[col + 1];
}
print_matrix(arr, rows, columns);
return 0;
}
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