Topic-Problem Solving on 2d arrays :video no-2

#1

what is wrong in this code? why it not generating sum as 16 when my input is
2 2
1 1
1 1

code:-
#include
using namespace std;

int main()
{
#ifndef ONLINE_JUDGE
freopen(“input.txt”, “r”, stdin);
freopen(“output.txt”, “w”, stdout);
#endif

int m, n;
cin >> m >> n;

int arr[m][n];

for (int i = 0; i < m; i++)
{
	for (int j = 0; j < n; j++)
	{
		cin >> arr[i][j];
	}
}


for (int i = 1; i < m; i++)
{
	for (int j = 0; j < n; j++)
	{
		arr[i][j] = arr[i][j] + arr[i - 1][j];
	}
}

for (int i = 0; i < m; i++)
{
	for (int j = 1; j < n; j++)
	{
		arr[i][j] = arr[i][j] + arr[i][j - 1];
	}
}

int sum = 0;

//for top left
for (int l_i = 0; l_i < m; l_i++)
{
	for (int l_j = 0; l_j < n; l_j++)
	{
		//For bottom right
		for (int r_i = l_i; r_i < m; r_i++)
		{
			for (int r_j = l_j; r_j < n; r_j++)
			{

				sum += ((arr[r_i][r_j]) - (arr[l_i - 1][r_j]) - (arr[r_i][l_j - 1]) + (arr[l_i - 1][l_j - 1]));
			}
		}
	}
}

cout << sum << endl;



return 0;

}

If the above code is wrong, plz provide me the correct code

#2

this line is incorrect
because if l_i is 0 then it will cause problem

correct way

sum += arr[r_i][r_j];
if (l_i > 0)
	sum -= (arr[l_i - 1][r_j]);
if (l_j > 0)
	sum -= (arr[r_i][l_j - 1]);
if (l_i > 0 && l_j > 0)
	sum += (arr[l_i - 1][l_j - 1]);
}

i hope you understood it
if yes then plz let me know

#3

#include
using namespace std;

int main()
{
#ifndef ONLINE_JUDGE
freopen(“input.txt”, “r”, stdin);
freopen(“output.txt”, “w”, stdout);
#endif

int m, n;
cin >> m >> n;

int arr[m][n];

for (int i = 0; i < m; i++)
{
	for (int j = 0; j < n; j++)
	{
		cin >> arr[i][j];
	}
}


for (int i = 1; i < m; i++)
{
	for (int j = 0; j < n; j++)
	{
		arr[i][j] = arr[i][j] + arr[i - 1][j];
	}
}

for (int i = 0; i < m; i++)
{
	for (int j = 1; j < n; j++)
	{
		arr[i][j] = arr[i][j] + arr[i][j - 1];
	}
}

int sum = 0;

//for top left
for (int l_i = 0; l_i < m; l_i++)
{
	for (int l_j = 0; l_j < n; l_j++)
	{
		//For bottom right
		for (int r_i = l_i; r_i < m; r_i++)
		{
			for (int r_j = l_j; r_j < n; r_j++)
			{

				sum += (arr[r_i][r_j]);
				if (l_i > 0)
				{
					sum -= (arr[l_i - 1][r_j]);
				}
				if (l_j > 0)
				{
					sum -= (arr[r_i][l_j - 1]);
				}
				if (l_j > 0 && r_j > 0)
				{
					sum += (arr[l_i - 1][l_j - 1]);
				}
			}
		}
	}
}

cout << sum << endl;



return 0;

}

I have corrected this . but for the input
2
1 1
1 1
sum should come as 16 but it is coming as 14.can you tell me where am i doing wrong?

#4

Modified Code

1 Like
#5

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