diff --git a/sik9252/LongestCommonPrefix.js b/sik9252/LongestCommonPrefix.js
new file mode 100644
index 0000000..2d71880
--- /dev/null
+++ b/sik9252/LongestCommonPrefix.js
@@ -0,0 +1,15 @@
+var longestCommonPrefix = function (strs) {
+  if (strs.length === 0) return "";
+
+  for (let i = 0; i < strs[0].length; i++) {
+    const char = strs[0][i];
+
+    for (let j = 1; j < strs.length; j++) {
+      if (strs[j][i] !== char) {
+        return strs[0].slice(0, i);
+      }
+    }
+  }
+
+  return strs[0];
+};
diff --git a/sik9252/SingleNumber.js b/sik9252/SingleNumber.js
new file mode 100644
index 0000000..4f035d3
--- /dev/null
+++ b/sik9252/SingleNumber.js
@@ -0,0 +1,11 @@
+var singleNumber = function (nums) {
+  const map = new Map();
+
+  for (const num of nums) {
+    map.set(num, (map.get(num) || 0) + 1);
+  }
+
+  for (const [num, count] of map) {
+    if (count === 1) return num;
+  }
+};