将一维数组转换为二维数组

Question

I am trying to print a 1D Array Given:

int[] D1 = new int[]{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25};
int n = 5;

My Expected Output is:

    {11,  7,  4,  2,  1},
    {16, 12,  8,  5,  3},
    {20, 17, 13,  9,  6},
    {23, 21, 18, 14, 10},
    {25, 24, 22, 19, 15}

This is my method:

cnt = 0;
for (int i = 0; i < n; i++) {
    for (int j = n-1; j >= 0; j--) {
        a[i][j] = D1[cnt];
        cnt++;
    }
}

which results in:

    { 5,  4,  3,  2,  1},
    {10,  9,  8,  7,  6},
    {15, 14, 13, 12, 11},
    {20, 19, 18, 17, 16},
    {25, 24, 23, 22, 21}

I'm having trouble assigning the correct positions, looking for help to correct this.

Answer 1

This has two sets of loops - one dealing with all the values to the top right of the diagonal (inclusive), and the second one the values to the bottom left of the diagonal. It is tested for sizes 4x4, 5x5 and 6x6.

public class SquareMatrix {

public static void main(String[] args) {
    //int[] D1 = new int[]{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16};
    int[] D1 = new int[]{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25};
    //int[] D1 = new int[]{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36};
    int n = 5;
    int[][] m = new int[n][n];

    int cnt = 0;
    // The top right part of the matrix (values 1-15 in a 5x5 scenario)
    for (int i = 1; i <= n; i++) {
        for (int j = 0; j < i; j++) {
            m[j][n+j-i] = D1[cnt++];
        }
    }
    // The bottom left of the matrix (values 16-25 in a 5x5 scenario)
    for (int i = n-1; i >= 1; i--) {
        for (int j = i; j >= 1; j--) {
            m[n-j][i-j] = D1[cnt++];
        }
    }
    printMatrix(m);
}

static void printMatrix(int[][] m) {
    for (int i = 0; i<m.length; i++) {
        for (int j = 0; j<m.length; j++) {
            System.out.printf("%2d ", m[i][j]);
        }
        System.out.println();
    }
}

}

producing for the 5x5:

11  7  4  2  1 
16 12  8  5  3 
20 17 13  9  6 
23 21 18 14 10 
25 24 22 19 15 

and 6x6

16 11  7  4  2  1 
22 17 12  8  5  3 
27 23 18 13  9  6 
31 28 24 19 14 10 
34 32 29 25 20 15 
36 35 33 30 26 21