How to reverse the rows of the matrix, if the sum row is less than the sum last column?-CodePudding

How can I reverse rows in a matrix, which sums less than the sum last column?
For example:

    1,2,3 -> sumRow1 = 6;
    4,5,6 -> sumRow2 = 15;
    7,8,9 -> sumRow3 = 24;
    sumLastCol = 18;
    row1 & row2 - reverse, row3 - unchange

Can I do it at once in the matrix or do I need to create a new array? This is my code, but it doesn't work correctly:

  public static void reverseMatrix(int n, int[][]randMatrix, int sumRow, int sumCol){
        for(int i=0; i<n; i  ){
            int start = 0;
            int end = n-1;
            if(sumRow<sumCol) {
                while (start < end) {
                    int temp = randMatrix[i][start];
                    randMatrix[i][start] = randMatrix[i][end];
                    randMatrix[i][end] = temp;
                    start  ;
                    end--;
                }
            }
        }
        for(int i=0; i<n; i  ){
            for(int j=0; j<n; j  ){
                System.out.print(randMatrix[i][j] "\t");
            }
            System.out.println();
        }
    }
    public static int sumLastColumn(int n, int[][]randMatrix){
        int sumCol = 0;
        for(int i=0; i<n; i  ){
            int[]row = randMatrix[i];
            sumCol  = row[row.length-1];
        }
        System.out.println("SumLastCol: " sumCol);
        return sumCol;
    }
    public static int sumRows(int n, int[][]randMatrix) {
        int sumRow = 0;
        for (int i=0; i<n; i  ) {
            sumRow = 0;
            for (int j=0; j<n; j  ) {
                sumRow = sumRow   randMatrix[i][j];
            }
            System.out.println("SumRow" (i 1) ": "   sumRow);
        }
        return sumRow;
    }
}

If you know how to do it, please help me:)

CodePudding user response：

Here's an easy way.

int[][] mat = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } };

First, compute the sum of the last column.

stream each row
map the last value in the row
and sum them.

int lastColSum = Arrays.stream(mat).mapToInt(s->s[s.length-1]).sum();

Now just iterate across the rows, summing them and comparing to the lastColSum and reverse if required.

for (int[] row :mat) {
    if (Arrays.stream(row).sum() < lastColSum) {
        reverse(row);
    }
}

for (int[] row :mat) {
    System.out.println(Arrays.toString(row));
}

prints

[3, 2, 1]
[6, 5, 4]
[7, 8, 9]

Helper method to reverse the row. It works by swapping values at it moves outside toward the middle. This works for even or odd length rows.

public static void reverse(int [] v) {
    for(int i = 0; i < v.length/2; i  ) {
        int t = v[0];
        v[0] = v[v.length-i-1];
        v[v.length-i-1] = t;
    }
}