I am trying to solve a problem where one two dimensional array(A) is
1 1 0
1 1 0
1 1 0
and the resulting two dimensional array(B) is
1 2 2
2 4 4
3 6 6
Each point in B is sum of corresponding entry in A, plus all entries to the left and above it.
Here is what I have done so far
public static void main(String[] args)
{
int[][] arrA = { { 1, 1,0 }, { 1, 1,0 },{ 1, 1,0 } };
int[][] arrB = new int [3] [3];
for (int i = 0; i < arrA.length; i++) {
for (int j = 0; j < arrA.length; j++) {
System.out.print(arrA[i][j] + " ");
}
System.out.println();
}
System.out.println();
for (int r=0; r<arrB.length; r++) {
for(int c=0; c<arrB[r].length; c++) {
arrB[r][c] = r * c;
}
}
for(int r=0; r < arrB.length; r++) {
for(int c=0; c < arrB[r].length; c++) {
// if((r==0 || r==(arrA.length-1)) || (c==0 || c==(arrA.length-1)) )
arrB[r][c] = r+c;
System.out.print(arrB[r][c]+" ");
}
System.out.println();
}
}
}
The answer I get is
0 1 2
1 2 3
2 3 4
The question I have is how can I get the correct numbers in array B. What code have I missed?
Each value of B
can be be calculated as :
B(i,j) = B(i-1,j-1) + B((i-1,j) - (i-1,j-1)) + A(i,j) + B((i,j-1)-(i-1,j-1))
This is because:
Diagonal value (i-1,j-1) is sum of all left and top value of (i,j) excluding immediate top and left values.
Left value (i, j-1) is sum of immediate left values + diagonal value.
Top value (i-1,j) is sum of immediate top values + diagonal values.
so, by combining these 3 values and the current element we get the value of B(i,j)
Here is the updated code :
public static void main(String args[]) {
int[][] arrA = { { 1, 1,0 }, { 1, 1,0 },{ 1, 1,0 } };
int [][]B = new int [3][3];
int diag, i, j,top,left;
int len = arrA.length;
int bredth = arrA[0].length;
for( i=0;i<len;i++){
for( j=0;j<bredth;j++) {
diag = 0; top=0; left=0;
if(i-1>=0 && j-1>=0) {
diag = B[i-1][j-1];
}
if(i-1>=0) {
top = B[i-1][j];
}
if(j-1>=0) {
left = B[i][j-1];
}
B[i][j] = diag + arrA[i][j] + (top-diag) + (left-diag);
}
}
for(i=0;i<3;i++) {
for(j=0;j<3;j++) {
System.out.print(B[i][j]);
}
System.out.println();
}
}
Issue with your code is you are just adding indexes
and not taking into consideration values
. But as per your question each value of B should be equal to sum of corresponding entry in A, plus all entries to the left and above it
for(int r=0; r < arrB.length; r++) {
for(int c=0; c < arrB[r].length; c++) {
// if((r==0 || r==(arrA.length-1)) || (c==0 || c==(arrA.length-1)) )
arrB[r][c] = r+c; //Here `r` and `c` are just indexes value not actual value
System.out.print(arrB[r][c]+" ");
}
System.out.println();
}
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