Added solutions

Author: nhistory

contains-duplicate/nhistoy.js

@@ -0,0 +1,24 @@
+/**
+ * @param {number[]} nums
+ * @return {boolean}
+ */
+var containsDuplicate = function (nums) {
+  // 1. Make hashmap that has previous value
+  let map = {};
+  // 2. Iterate nums to check nums[i] is duplicated or not
+  for (let i = 0; i < nums.length; i++) {
+    // 2.1 Check there is same value on the map
+    // 3. Return true when their is duplicated value
+    if (nums[i] in map) {
+      return true;
+    } else map[nums[i]] = i;
+  }
+  return false;
+};
+
+// TC: O(n)
+// SC: O(n)
+
+console.log(containsDuplicate([1, 2, 3, 1])); // true
+console.log(containsDuplicate([1, 2, 3, 4])); // false
+console.log(containsDuplicate([1, 1, 1, 3, 3, 4, 3, 2, 4, 2])); // true

two-sum/nhistory.js

@@ -0,0 +1,23 @@
+/**
+ * @param {number[]} nums
+ * @param {number} target
+ * @return {number[]}
+ */
+var twoSum = function (nums, target) {
+  // 1. Make a Hashmap to store { key(index) : value(target-num)}
+  let map = {};
+  // 2. Iterate to find value is equal to (target - nums[i])
+  // There is only one solution
+  for (let i = 0; i < nums.length; i++) {
+    const diff = target - nums[i];
+    // 3. If there is an index that has different value, return array
+    if (diff in map) return [map[diff], i];
+    map[nums[i]] = i;
+  }
+};
+
+// TC: O(n)
+// SC: O(n)
+
+console.log(twoSum([2, 7, 11, 15], 9));
+console.log(twoSum([3, 2, 4], 6));