Similar to Find K Pairs with Smallest Sums.

```
public class Solution {
public int kthSmallest(final int[][] matrix, int k) {
int c = 0;
PriorityQueue<int[]> queue = new PriorityQueue<>(
k, (o1, o2) -> matrix[o1[0]][o1[1]] - matrix[o2[0]][o2[1]]);
queue.offer(new int[] {0, 0});
while (true) {
int[] pair = queue.poll();
if (++c == k) {
return matrix[pair[0]][pair[1]];
}
if (pair[0] == 0 && pair[1] + 1 < matrix[0].length) {
queue.offer(new int[] {0, pair[1] + 1});
}
if (pair[0] + 1 < matrix.length) {
queue.offer(new int[] {pair[0] + 1, pair[1]});
}
}
}
}
```