diff --git a/find-median-from-data-stream/hsskey.js b/find-median-from-data-stream/hsskey.js
new file mode 100644
index 000000000..a408d1290
--- /dev/null
+++ b/find-median-from-data-stream/hsskey.js
@@ -0,0 +1,101 @@
+class Heap {
+    constructor(compare) {
+        this.data = [];
+        this.compare = compare;
+    }
+
+    size() {
+        return this.data.length;
+    }
+
+    peek() {
+        return this.data[0];
+    }
+
+    push(val) {
+        this.data.push(val);
+        this._siftUp();
+    }
+
+    pop() {
+        const top = this.peek();
+        const bottom = this.data.pop();
+        if (this.data.length > 0) {
+            this.data[0] = bottom;
+            this._siftDown();
+        }
+        return top;
+    }
+
+    _siftUp() {
+        let i = this.data.length - 1;
+        const node = this.data[i];
+        while (i > 0) {
+            const parent = Math.floor((i - 1) / 2);
+            if (this.compare(node, this.data[parent])) {
+                this.data[i] = this.data[parent];
+                i = parent;
+            } else break;
+        }
+        this.data[i] = node;
+    }
+
+    _siftDown() {
+        let i = 0;
+        const node = this.data[0];
+        const length = this.data.length;
+
+        while (true) {
+            let left = 2 * i + 1;
+            let right = 2 * i + 2;
+            let swap = i;
+
+            if (left < length && this.compare(this.data[left], this.data[swap])) {
+                swap = left;
+            }
+            if (right < length && this.compare(this.data[right], this.data[swap])) {
+                swap = right;
+            }
+            if (swap === i) break;
+
+            this.data[i] = this.data[swap];
+            i = swap;
+        }
+
+        this.data[i] = node;
+    }
+}
+
+var MedianFinder = function() {
+    this.small = new Heap((a, b) => a > b); // max heap
+    this.large = new Heap((a, b) => a < b); // min heap
+};
+
+MedianFinder.prototype.addNum = function(num) {
+    this.small.push(num);
+
+    if (
+        this.small.size() > 0 &&
+        this.large.size() > 0 &&
+        this.small.peek() > this.large.peek()
+    ) {
+        this.large.push(this.small.pop());
+    }
+
+    if (this.small.size() > this.large.size() + 1) {
+        this.large.push(this.small.pop());
+    }
+    if (this.large.size() > this.small.size() + 1) {
+        this.small.push(this.large.pop());
+    }
+};
+
+MedianFinder.prototype.findMedian = function() {
+    if (this.small.size() > this.large.size()) {
+        return this.small.peek();
+    }
+    if (this.large.size() > this.small.size()) {
+        return this.large.peek();
+    }
+    return (this.small.peek() + this.large.peek()) / 2;
+};
diff --git a/insert-interval/hsskey.js b/insert-interval/hsskey.js
new file mode 100644
index 000000000..6945337d9
--- /dev/null
+++ b/insert-interval/hsskey.js
@@ -0,0 +1,25 @@
+/**
+ * @param {number[][]} intervals
+ * @param {number[]} newInterval
+ * @return {number[][]}
+ */
+var insert = function(intervals, newInterval) {
+    const res = [];
+
+    for (let i = 0; i < intervals.length; i++) {
+        if (newInterval[1] < intervals[i][0]) {
+            res.push(newInterval);
+            return res.concat(intervals.slice(i));
+        } else if (newInterval[0] > intervals[i][1]) {
+            res.push(intervals[i]);
+        } else {
+            newInterval = [
+                Math.min(newInterval[0], intervals[i][0]),
+                Math.max(newInterval[1], intervals[i][1])
+            ];
+        }
+    }
+
+    res.push(newInterval);
+    return res;
+};
diff --git a/kth-smallest-element-in-a-bst/hsskey.js b/kth-smallest-element-in-a-bst/hsskey.js
new file mode 100644
index 000000000..3a6643250
--- /dev/null
+++ b/kth-smallest-element-in-a-bst/hsskey.js
@@ -0,0 +1,36 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val === undefined ? 0 : val);
+ *     this.left = (left === undefined ? null : left);
+ *     this.right = (right === undefined ? null : right);
+ * }
+ */
+
+/**
+ * @param {TreeNode} root
+ * @param {number} k
+ * @return {number}
+ */
+var kthSmallest = function(root, k) {
+    let n = 0;
+    const stack = [];
+    let cur = root;
+
+    while (cur || stack.length > 0) {
+        while (cur) {
+            stack.push(cur);
+            cur = cur.left;
+        }
+
+        cur = stack.pop();
+        n += 1;
+        if (n === k) {
+            return cur.val;
+        }
+
+        cur = cur.right;
+    }
+
+    return -1;
+};
diff --git a/lowest-common-ancestor-of-a-binary-search-tree/hsskey.js b/lowest-common-ancestor-of-a-binary-search-tree/hsskey.js
new file mode 100644
index 000000000..8c1a651bd
--- /dev/null
+++ b/lowest-common-ancestor-of-a-binary-search-tree/hsskey.js
@@ -0,0 +1,29 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+
+/**
+ * @param {TreeNode} root
+ * @param {TreeNode} p
+ * @param {TreeNode} q
+ * @return {TreeNode}
+ */
+var lowestCommonAncestor = function(root, p, q) {
+    let cur = root;
+
+    while (cur) {
+        if (p.val > cur.val && q.val > cur.val) {
+            cur = cur.right;
+        } else if (p.val < cur.val && q.val < cur.val) {
+            cur = cur.left;
+        } else {
+            return cur;
+        }
+    }
+
+    return null;
+};
diff --git a/meeting-rooms/hsskey.js b/meeting-rooms/hsskey.js
new file mode 100644
index 000000000..8789afba9
--- /dev/null
+++ b/meeting-rooms/hsskey.js
@@ -0,0 +1,36 @@
+import {
+    Interval,
+} from '/opt/node/lib/lintcode/index.js';
+
+/**
+ * Definition of Interval:
+ * class Interval {
+ *   constructor(start, end) {
+ *     this.start = start;
+ *     this.end = end;
+ *   }
+ * }
+ */
+
+export class Solution {
+    /**
+     * @param {Interval[]} intervals - an array of meeting time intervals
+     * @return {boolean} - whether a person could attend all meetings
+     */
+    canAttendMeetings(intervals) {
+        // start 기준으로 정렬
+        intervals.sort((a, b) => a.start - b.start);
+
+        // 연속된 회의의 시간 비교
+        for (let i = 1; i < intervals.length; i++) {
+            const prev = intervals[i - 1];
+            const curr = intervals[i];
+
+            if (prev.end > curr.start) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+}