[Sehwan]Added solutions for week1

contains-duplicate/nhistoy.js

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+/**
+ * @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

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+/**
+ * @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));

valid-anagram/nhistory.js

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+/**
+ * @param {string} s
+ * @param {string} t
+ * @return {boolean}
+ */
+var isAnagram = function (s, t) {
+  /*
+    // Split string and sort charaters
+    // Compare s and t after sorting
+    return s.split("").sort().join() === t.split("").sort().join()
+    // 92ms, 53.29MB
+    */
+
+  // Made Hashmap and count number of each charater
+  let map = {};
+
+  // Check character length between s and t
+  if (s.length !== t.length) return false;
+  // Put a character and add or substract number
+  for (let i = 0; i < s.length; i++) {
+    map[s[i]] = map[s[i]] ? map[s[i]] + 1 : 1;
+    map[t[i]] = map[t[i]] ? map[t[i]] - 1 : -1;
+  }
+
+  for (let i = 0; i < s.length; i++) {
+    if (map[s[i]] !== 0) return false;
+  }
+
+  return true;
+};
+
+console.log(isAnagram("anagram", "nagaram"));
+console.log(isAnagram("rat", "car"));
+
+// TC: O(n)
+// SC: O(n)