feat: 23. Merge k Sorted Lists

Author: gwbaik9717

merge-k-sorted-lists/gwbaik9717.js

@@ -0,0 +1,134 @@
+// k: len(lists), n: Total number of nodes
+// Time complexity: O(nlogk)
+// Space complexity: O(n)
+
+class MinHeap {
+  constructor() {
+    this.heap = [null];
+  }
+
+  isEmpty() {
+    return this.heap.length === 1;
+  }
+
+  push(listNode) {
+    this.heap.push(listNode);
+
+    let current = this.heap.length - 1;
+    let parent = Math.floor(current / 2);
+
+    while (parent !== 0) {
+      if (this.heap[parent].val > listNode.val) {
+        [this.heap[parent], this.heap[current]] = [
+          this.heap[current],
+          this.heap[parent],
+        ];
+
+        current = parent;
+        parent = Math.floor(current / 2);
+        continue;
+      }
+
+      break;
+    }
+  }
+
+  pop() {
+    if (this.heap.length === 1) {
+      return;
+    }
+
+    if (this.heap.length === 2) {
+      return this.heap.pop();
+    }
+
+    const rv = this.heap[1];
+
+    this.heap[1] = this.heap.pop();
+
+    let current = 1;
+    let left = current * 2;
+    let right = left + 1;
+
+    while (
+      (this.heap[left] && this.heap[current].val > this.heap[left].val) ||
+      (this.heap[right] && this.heap[current].val > this.heap[right].val)
+    ) {
+      if (this.heap[left] && this.heap[right]) {
+        if (this.heap[left].val < this.heap[right].val) {
+          [this.heap[left], this.heap[current]] = [
+            this.heap[current],
+            this.heap[left],
+          ];
+          current = left;
+        } else {
+          [this.heap[right], this.heap[current]] = [
+            this.heap[current],
+            this.heap[right],
+          ];
+          current = right;
+        }
+
+        left = current * 2;
+        right = left + 1;
+        continue;
+      }
+
+      [this.heap[left], this.heap[current]] = [
+        this.heap[current],
+        this.heap[left],
+      ];
+      current = left;
+      left = current * 2;
+      right = left + 1;
+    }
+
+    return rv;
+  }
+}
+
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * @param {ListNode[]} lists
+ * @return {ListNode}
+ */
+var mergeKLists = function (lists) {
+  const minHeap = new MinHeap();
+
+  for (const list of lists) {
+    if (list) {
+      minHeap.push(list);
+    }
+  }
+
+  let answer = null;
+  let next = null;
+
+  while (!minHeap.isEmpty()) {
+    const current = minHeap.pop();
+
+    if (!answer) {
+      answer = new ListNode();
+      next = answer;
+    }
+
+    next.val = current.val;
+
+    if (current.next) {
+      minHeap.push(current.next);
+    }
+
+    if (!minHeap.isEmpty()) {
+      next.next = new ListNode();
+      next = next.next;
+    }
+  }
+
+  return answer;
+};