排序数组的合并？

Question

I have a matrix with sorted rows. Now I want kind of merge sort for my columns (I want to save numbers in a different array ascending). Is there any efficient solution for that?

I don't want to go through the hole matrix to find the minimum.

Answer 1

Well, if your rows are sorted, then you don't really need to traverse through whole matrix every time. You only need to traverse 1 column each time you pick a minimal value and keep track of separate indexes for each row.

Meaning something like this:

int newSize = rows * cols;
int[] indexes = new int[rows];
double[] sortedArray = new double[newSize];
for (int i = 0; i < newSize; i++){
    int minIndex = -1;
    double minValue = Double.MAX_VALUE;
    for (int j = 0; j < rows; j++) {
        if (indexes[j] < cols && matrix[j][indexes[j]] < minValue){
            minValue = matrix[j][indexes[j]];
            minIndex = j;
        }
    }
    sortedArray[i] = minValue;
    indexes[minIndex]++;
}

example input

double[][] matrix = {
    { 1,   4, 100},
    { 5,  10,  13},
    {11,  40,  55},
    { 0,   6,  10}
};

Output

[0.0, 1.0, 4.0, 5.0, 6.0, 10.0, 10.0, 11.0, 13.0, 40.0, 55.0, 100.0]