diff --git a/contains-duplicate/yuhyeon99.js b/contains-duplicate/yuhyeon99.js
new file mode 100644
index 0000000000..19d3603784
--- /dev/null
+++ b/contains-duplicate/yuhyeon99.js
@@ -0,0 +1,12 @@
+/**
+ * @param {number[]} nums
+ * @return {boolean}
+ */
+var containsDuplicate = function(nums) {
+    let numsSet = new Set();
+    for(let i = 0; i < nums.length; i ++) {
+        if(numsSet.has(nums[i])) return true;
+        numsSet.add(nums[i])
+    }
+    return false;
+};
diff --git a/house-robber/yuhyeon99.js b/house-robber/yuhyeon99.js
new file mode 100644
index 0000000000..2165fcc428
--- /dev/null
+++ b/house-robber/yuhyeon99.js
@@ -0,0 +1,19 @@
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var rob = function(nums) {
+    const memo = {};
+
+    function dfs(start) {
+        if(memo[start] !== undefined) return memo[start];
+        if(start >= nums.length) {
+            memo[start] = 0;
+        } else {
+            memo[start] = Math.max(nums[start] + dfs(start + 2), dfs(start + 1))
+        }
+        return memo[start];
+    }
+
+    return dfs(0);
+};
diff --git a/longest-consecutive-sequence/yuhyeon99.js b/longest-consecutive-sequence/yuhyeon99.js
new file mode 100644
index 0000000000..c0fed7079e
--- /dev/null
+++ b/longest-consecutive-sequence/yuhyeon99.js
@@ -0,0 +1,25 @@
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var longestConsecutive = function(nums) {
+    if(!nums.length) return 0;
+
+    nums.sort((a, b) => a - b);
+    var answer = 0;
+    var length = 1;
+    for(let i = 0; i < nums.length - 1; i ++) {
+        if(nums[i] === nums[i + 1]) {
+            continue;
+        } else if (nums[i] + 1 === nums[i + 1]) {
+            length ++;
+        } else {
+            answer = Math.max(length, answer);
+            length = 1;
+        }
+    }
+
+    answer = Math.max(length, answer);
+
+    return answer;
+};
diff --git a/top-k-frequent-elements/yuhyeon99.js b/top-k-frequent-elements/yuhyeon99.js
new file mode 100644
index 0000000000..f21a9691be
--- /dev/null
+++ b/top-k-frequent-elements/yuhyeon99.js
@@ -0,0 +1,21 @@
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number[]}
+ */
+var topKFrequent = function(nums, k) {
+    var dict = {};
+    var sortTable = [];
+    for(let i = 0; i < nums.length; i ++) {
+        dict[nums[i]] = dict[nums[i]] ? dict[nums[i]] + 1 : 1;
+    }
+    
+    for(let ele in dict) {
+        sortTable.push([ele, dict[ele]]);
+    }
+    sortTable.sort((a, b) => {
+        return b[1] - a[1];
+    });
+
+    return sortTable.slice(0, k).map(e => Number(e[0]))
+};
diff --git a/two-sum/yuhyeon99.js b/two-sum/yuhyeon99.js
new file mode 100644
index 0000000000..9fd5413bd6
--- /dev/null
+++ b/two-sum/yuhyeon99.js
@@ -0,0 +1,35 @@
+/**
+ * 정수 배열 두 숫자를 합쳐서 target의 값이 나오게 해야함
+ * 해당하는 인덱스를 길이가 2인 배열로 반환하시오.
+ * 각 정수는 한 번씩만 쓸 수 있음.
+ * 
+ * @param {number[]} nums
+ * @param {number} target
+ * @return {number[]}
+ */
+var twoSum = function(nums, target) {
+    const numsMap = new Map();
+
+    nums.forEach((num, i) => {
+        if(!numsMap.has(num)) numsMap.set(num, []);
+        numsMap.get(num).push(i);
+    });
+
+    for(let i = 0; i < nums.length; i ++) {
+        for(let j = i + 1; j < nums.length; j ++) {
+            if(nums[i] + nums[j] === target) {
+                if(hasMultipleEntries(numsMap.get(nums[i]))) {
+                    return [...numsMap.get(nums[i]).slice(0,2)];
+                } else {
+                    return [...numsMap.get(nums[i]), ...numsMap.get(nums[j])];
+                }
+            }
+        }
+    }
+
+    return;
+};
+
+function hasMultipleEntries(arr) {
+    return arr.length >= 2;
+}