diff --git a/doitchuu/LongestCommonPrefix.js b/doitchuu/LongestCommonPrefix.js
new file mode 100644
index 0000000..78bbc4c
--- /dev/null
+++ b/doitchuu/LongestCommonPrefix.js
@@ -0,0 +1,21 @@
+/**
+ * @param {string[]} strs
+ * @return {string}
+ */
+var longestCommonPrefix = function(strs) {
+    let prefix = "";
+
+    for (let i = 0; i < strs[0].length; i++) {
+        const current = strs[0][i];
+
+        for (let j = 1; j < strs.length; j++) {
+            if (strs[j][i] !== current) {
+                return prefix;
+            }
+        }
+
+        prefix += current;
+    }
+
+    return prefix;
+};
diff --git a/doitchuu/SingleNumber.js b/doitchuu/SingleNumber.js
new file mode 100644
index 0000000..3622a32
--- /dev/null
+++ b/doitchuu/SingleNumber.js
@@ -0,0 +1,17 @@
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var singleNumber = function(nums) {
+    const map = new Map();
+
+    for (let i = 0; i < nums.length; i++) {
+        map.set(nums[i], (map.get(nums[i]) || 0) + 1);
+    }
+
+    for (const [key, value] of map) {
+        if (value === 1) {
+            return key;
+        }
+    }
+};