diff --git a/oh-chaeyeon/2013_Detect_Squares.js b/oh-chaeyeon/2013_Detect_Squares.js
new file mode 100644
index 0000000..69f967c
--- /dev/null
+++ b/oh-chaeyeon/2013_Detect_Squares.js
@@ -0,0 +1,50 @@
+var DetectSquares = function () {
+  this.pointCount = new Map();
+};
+
+/**
+ * @param {number[]} point
+ * @return {void}
+ */
+DetectSquares.prototype.add = function (point) {
+  const [x, y] = point;
+  const key = `${x},${y}`;
+  this.pointCount.set(key, (this.pointCount.get(key) || 0) + 1);
+};
+
+/**
+ * @param {number[]} point
+ * @return {number}
+ */
+DetectSquares.prototype.count = function (point) {
+  const [x, y] = point;
+  let totalSquares = 0;
+
+  for (const key of this.pointCount.keys()) {
+    const [px, py] = key.split(",").map(Number);
+
+    if (Math.abs(px - x) !== Math.abs(py - y) || px === x || py === y) continue;
+
+    const corner1 = `${px},${y}`;
+    const corner2 = `${x},${py}`;
+
+    const countCurrent = this.pointCount.get(key) || 0;
+    const countCorner1 = this.pointCount.get(corner1) || 0;
+    const countCorner2 = this.pointCount.get(corner2) || 0;
+
+    totalSquares += countCurrent * countCorner1 * countCorner2;
+  }
+
+  return totalSquares;
+};
+
+/**
+ * Your DetectSquares object will be instantiated and called as such:
+ * var obj = new DetectSquares()
+ * obj.add(point)
+ * var param_2 = obj.count(point)
+ */
+
+// Time taken : 57m 48s
+// Runtime : 336ms
+// Memory : 62.48MB
diff --git a/oh-chaeyeon/39_Combination_Sum.js b/oh-chaeyeon/39_Combination_Sum.js
new file mode 100644
index 0000000..e5913bb
--- /dev/null
+++ b/oh-chaeyeon/39_Combination_Sum.js
@@ -0,0 +1,24 @@
+/**
+ * @param {number[]} candidates
+ * @param {number} target
+ * @return {number[][]}
+ */
+var combinationSum = function (candidates, target) {
+  const dp = Array.from({ length: target + 1 }, () => []);
+  dp[0] = [[]];
+
+  for (let i = 0; i < candidates.length; i++) {
+    for (let j = candidates[i]; j <= target; j++) {
+      const combinations = dp[j - candidates[i]];
+      for (const combination of combinations) {
+        dp[j].push([...combination, candidates[i]]);
+      }
+    }
+  }
+
+  return dp[target];
+};
+
+// Time taken : 33m 36s
+// Runtime : 6ms
+// Memory : 57.15MB
diff --git a/oh-chaeyeon/57_Insert_Interval.JS b/oh-chaeyeon/57_Insert_Interval.JS
new file mode 100644
index 0000000..fa7740b
--- /dev/null
+++ b/oh-chaeyeon/57_Insert_Interval.JS
@@ -0,0 +1,32 @@
+/**
+ * @param {number[][]} intervals
+ * @param {number[]} newInterval
+ * @return {number[][]}
+ */
+var insert = function (intervals, newInterval) {
+  const result = [];
+  let i = 0;
+
+  while (i < intervals.length && intervals[i][1] < newInterval[0]) {
+    result.push(intervals[i]);
+    i++;
+  }
+
+  while (i < intervals.length && intervals[i][0] <= newInterval[1]) {
+    newInterval[0] = Math.min(newInterval[0], intervals[i][0]);
+    newInterval[1] = Math.max(newInterval[1], intervals[i][1]);
+    i++;
+  }
+  result.push(newInterval);
+
+  while (i < intervals.length) {
+    result.push(intervals[i]);
+    i++;
+  }
+
+  return result;
+};
+
+// Time taken : 24m 13s
+// Runtime : 4ms
+// Memory : 54.67MB
diff --git a/oh-chaeyeon/743_Network_Delay_Time.js b/oh-chaeyeon/743_Network_Delay_Time.js
new file mode 100644
index 0000000..6b99a7d
--- /dev/null
+++ b/oh-chaeyeon/743_Network_Delay_Time.js
@@ -0,0 +1,25 @@
+/**
+ * @param {number[][]} times
+ * @param {number} n
+ * @param {number} k
+ * @return {number}
+ */
+var networkDelayTime = function (times, n, k) {
+  const minTime = new Array(n + 1).fill(Infinity);
+  minTime[k] = 0;
+
+  for (let i = 1; i < n; i++) {
+    for (const [u, v, w] of times) {
+      if (minTime[u] !== Infinity && minTime[u] + w < minTime[v]) {
+        minTime[v] = minTime[u] + w;
+      }
+    }
+  }
+
+  const maxTime = Math.max(...minTime.slice(1));
+  return maxTime === Infinity ? -1 : maxTime;
+};
+
+// Time taken : 1h 20m
+// Runtime : 103ms
+// Memory : 57.07MB
diff --git a/oh-chaeyeon/7_Reverse_integer.js b/oh-chaeyeon/7_Reverse_integer.js
new file mode 100644
index 0000000..6fadf6c
--- /dev/null
+++ b/oh-chaeyeon/7_Reverse_integer.js
@@ -0,0 +1,26 @@
+/**
+ * @param {number} x
+ * @return {number}
+ */
+var reverse = function (x) {
+  let num = 0;
+  const INT_MIN = -Math.pow(2, 31);
+  const INT_MAX = Math.pow(2, 31) - 1;
+
+  while (x !== 0) {
+    let digit = x % 10;
+    x = (x - digit) / 10;
+
+    num = num * 10 + digit;
+
+    if (num < INT_MIN || num > INT_MAX) {
+      return 0;
+    }
+  }
+
+  return num;
+};
+
+// Time taken : 30m+
+// Runtime : 59ms (73ms)
+// Memory : 53.55MB