Sudoku Validator - CodinGame | C++ Implementation
The problem is from CodinGame with difficulty level Easy.
Problem:
A sudoku grid consists of 9*9 = 81 cells split in 9 sub-grids of 3*3 = 9 cells.
For the grid to be correct, each row must contain one occurrence of each digit(1 to 9), each column must contain one occurrence of each digit (1 to 9) and each sub-grid must contain one occurrence of each digit (1 to 9).
You shall answer true if the grid is correct or false if it is not.
Read full problem here : Sudoku Validator
Solution:
To verify that each row contains only one occurrence of each digit (1 to 9) , we will make an array which will verify that the count of each digit is one. If the count of any digit is more than 1 than the function returns false.
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bool status = true;
for (int i = 0; i < 9; ++i)
{
std::vector<bool> row_values(9, false);
for (int r = 0; r < 9; ++r)
{
if (row_values[grid[r][i] - 1] == false)
{
row_values[grid[r][i] - 1] = true;
}
else
{
status = false;
return status;
}
}
}
Here, array row_values makes sure that count of each digit is one.
Similarly, we will verify for each column.
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bool status = true;
for (int i = 0; i < 9; ++i)
{
std::vector<bool> col_values(9, false);
for (int c = 0; c < 9; ++c)
{
if (col_values[grid[i][c] - 1] == false)
{
col_values[grid[i][c] - 1] = true;
}
else
{
status = false;
return status;
}
}
}
Here, array col_values makes sure that count of each digit is one.
To verify diagonal subgrids, this code is used. It happens when i == 0 or i % 3 == 0.
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bool status = true;
for (int i = 0; i < 9; ++i)
{
std::vector<bool> subgrid_values(9, false);
for (int r_sub = i; r_sub < i+3; ++r_sub)
{
for (int c_sub = i; c_sub < i+3; ++c_sub)
{
if (subgrid_values[grid[r_sub][c_sub] - 1] == false)
{
subgrid_values[grid[r_sub][c_sub] - 1] = true;
}
else
{
status = false;
return status;
}
}
}
}
To verify these subgrids, this code is used. It happens when i % 3 == 0.
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bool status = true;
for (int i = 0; i < 9; ++i)
{
std::vector<bool> subgrid_values(9, false);
for (int r_sub = i; r_sub < i+3; ++r_sub)
{
for(int c_sub = 0; c_sub < 3; ++c_sub)
{
if (subgrid_values[grid[r_sub][c_sub] - 1] == false)
{
subgrid_values[grid[r_sub][c_sub] - 1] = true;
}
else
{
status = false;
return status;
}
}
}
std::fill(subgrid_values.begin(), subgrid_values.end(), false);
for (int r_sub = 0; r_sub < 3; ++r_sub)
{
for(int c_sub = i; c_sub < i+3; ++c_sub)
{
if (subgrid_values[grid[r_sub][c_sub] - 1] == false)
{
subgrid_values[grid[r_sub][c_sub] - 1] = true;
}
else
{
status = false;
return status;
}
}
}
std::fill(subgrid_values.begin(), subgrid_values.end(), false);
}
To verify these subgrids, this code is used. It happens when i == 6.
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bool status = true;
for (int i = 0; i < 9; ++i)
{
std::vector<bool> subgrid_values(9, false);
for (int r_sub = i; r_sub < i+3; ++r_sub)
{
for(int c_sub = 3; c_sub < 6; ++c_sub)
{
if (subgrid_values[grid[r_sub][c_sub] - 1] == false)
{
subgrid_values[grid[r_sub][c_sub] - 1] = true;
}
else
{
status = false;
return status;
}
}
}
std::fill(subgrid_values.begin(), subgrid_values.end(), false);
for (int r_sub = 3; r_sub < 6; ++r_sub)
{
for(int c_sub = i; c_sub < i+3; ++c_sub)
{
if (subgrid_values[grid[r_sub][c_sub] - 1] == false)
{
subgrid_values[grid[r_sub][c_sub] - 1] = true;
}
else
{
status = false;
return status;
}
}
}
}
Since in one iteration more than one subgrids are checked. So we have to reinitialize array to its initial state using fill(subgrid_values.begin(), subgrid_values.end(), false)
C++ Implementation
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#include <iostream>
#include <vector>
#include <algorithm>
bool sudoku_validator(std::vector<std::vector<int>>& grid)
{
bool status = true;
for (int i = 0; i < 9; ++i)
{
std::vector<bool> row_values(9, false);
std::vector<bool> col_values(9, false);
std::vector<bool> subgrid_values(9, false);
for (int r = 0; r < 9; ++r)
{
if (row_values[grid[r][i] - 1] == false)
{
row_values[grid[r][i] - 1] = true;
}
else
{
status = false;
return status;
}
}
for (int c = 0; c < 9; ++c)
{
if (col_values[grid[i][c] - 1] == false)
{
col_values[grid[i][c] - 1] = true;
}
else
{
status = false;
return status;
}
}
if (i == 0)
{
for (int r_sub = i; r_sub < i+3; ++r_sub)
{
for (int c_sub = i; c_sub < i+3; ++c_sub)
{
if (subgrid_values[grid[r_sub][c_sub] - 1] == false)
{
subgrid_values[grid[r_sub][c_sub] - 1] = true;
}
else
{
status = false;
return status;
}
}
}
}
else if (i % 3 == 0)
{
for (int r_sub = i; r_sub < i+3; ++r_sub)
{
for(int c_sub = 0; c_sub < 3; ++c_sub)
{
if (subgrid_values[grid[r_sub][c_sub] - 1] == false)
{
subgrid_values[grid[r_sub][c_sub] - 1] = true;
}
else
{
status = false;
return status;
}
}
}
std::fill(subgrid_values.begin(), subgrid_values.end(), false);
for (int r_sub = 0; r_sub < 3; ++r_sub)
{
for(int c_sub = i; c_sub < i+3; ++c_sub)
{
if (subgrid_values[grid[r_sub][c_sub] - 1] == false)
{
subgrid_values[grid[r_sub][c_sub] - 1] = true;
}
else
{
status = false;
return status;
}
}
}
std::fill(subgrid_values.begin(), subgrid_values.end(), false);
if (i == 6)
{
for (int r_sub = i; r_sub < i+3; ++r_sub)
{
for(int c_sub = 3; c_sub < 6; ++c_sub)
{
if (subgrid_values[grid[r_sub][c_sub] - 1] == false)
{
subgrid_values[grid[r_sub][c_sub] - 1] = true;
}
else
{
status = false;
return status;
}
}
}
std::fill(subgrid_values.begin(), subgrid_values.end(), false);
for (int r_sub = 3; r_sub < 6; ++r_sub)
{
for(int c_sub = i; c_sub < i+3; ++c_sub)
{
if (subgrid_values[grid[r_sub][c_sub] - 1] == false)
{
subgrid_values[grid[r_sub][c_sub] - 1] = true;
}
else
{
status = false;
return status;
}
}
}
}
std::fill(subgrid_values.begin(), subgrid_values.end(), false);
for (int r_sub = i; r_sub < i+3; ++r_sub)
{
for (int c_sub = i; c_sub < i+3; ++c_sub)
{
if (subgrid_values[grid[r_sub][c_sub] - 1] == false)
{
subgrid_values[grid[r_sub][c_sub] - 1] = true;
}
else
{
status = false;
return status;
}
}
}
}
}
return status;
}
int main()
{
std::vector< std::vector<int> > sudoku_grid;
for (int i = 0; i < 9; i++)
{
std::vector<int> row;
for (int j = 0; j < 9; j++)
{
int n;
std::cin >> n; std::cin.ignore();
row.push_back(n);
}
sudoku_grid.push_back(row);
}
bool result = sudoku_validator(sudoku_grid);
if (result)
{
std::cout << "true\n";
}
else
{
std::cout << "false\n";
}
}
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