One-Hundred-Seventy-Nine Commit: Add Kth Smallest Number in M Sorted Lists problem to K-Way Merge section

Author: AAdewunmi

src/K_Way_Merge/Problem_2_Kth_Smallest_Number_In_M_Sorted_List.java

@@ -0,0 +1,51 @@
+package K_Way_Merge;
+
+// Problem Statement: Kth Smallest Number in M Sorted Lists (medium)
+// LeetCode Question:
+
+import java.util.List;
+import java.util.PriorityQueue;
+
+public class Problem_2_Kth_Smallest_Number_In_M_Sorted_List {
+
+    class Node {
+        int elementIndex;
+        int arrayIndex;
+
+        Node(int elementIndex, int arrayIndex) {
+            this.elementIndex = elementIndex;
+            this.arrayIndex = arrayIndex;
+        }
+    }
+
+    public int findKthSmallest(List<List<Integer>> lists, int k) {
+        PriorityQueue<Node> minHeap = new PriorityQueue<>(
+                (n1, n2) -> lists.get(n1.arrayIndex).get(n1.elementIndex)
+                        - lists.get(n2.arrayIndex).get(n2.elementIndex));
+
+        // put the 1st element of each list in the min heap
+        for (int i = 0; i < lists.size(); i++) {
+            if (!lists.get(i).isEmpty()) {
+                minHeap.add(new Node(0, i));
+            }
+        }
+
+        // take the smallest (top) element from the min heap, if the running count is equal
+        // to k, return the number; if the list of the top element has more elements, add the
+        // next element to the heap
+        int numberCount = 0, result = 0;
+        while (!minHeap.isEmpty()) {
+            Node node = minHeap.poll();
+            result = lists.get(node.arrayIndex).get(node.elementIndex);
+            if (++numberCount == k) {
+                break;
+            }
+            node.elementIndex++;
+            if (node.elementIndex < lists.get(node.arrayIndex).size()) {
+                minHeap.add(node);
+            }
+        }
+        return result;
+    }
+
+}