Solving https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/submissions/

Solution.kt

import java.util.PriorityQueue

class Solution {
    data class Entry(val row: Int, val col: Int, val num: Int)
    
    fun kthSmallest(matrix: Array<IntArray>, k: Int): Int {
        val q = PriorityQueue<Entry>(1, { x, y -> x.num - y.num })
        matrix.forEachIndexed{ i, row -> q.add(Entry(i, 0, row.get(0))) }

        var nth: Int = 0
        var nthMin: Int = Int.MIN_VALUE
        while (!q.isEmpty()) {
            val e = q.poll()
            nth++
            nthMin = e.num
            if (nth == k) {
                return nthMin
            }
            
            if (e.col + 1 < matrix.size) {
                val r = e.row
                val c = e.col + 1
                q.add(Entry(r, c, matrix[r][c]))
            }
        }
        return nthMin
    }
}