[heesun-task] WEEK 01 solutions

contains-duplicate/heesun-task.js

@@ -0,0 +1,26 @@
+/**
+ * @param {number[]} nums
+ * @return {boolean}
+ */
+ /*
+    Goal: return true if duplicated #, false if no duplicated number
+
+    Plan:
+    - create a Set
+    - loop num in nums
+        - num exists in the Set -> return true
+        - not exsits ->  add the num in the Set, continue to the next loop
+    - return false 
+
+    space complexity: O(n)
+    time complexity: O(n)
+  */
+var containsDuplicate = function(nums) {
+    const seen = new Set();
+
+    for(const num of nums) {
+        if (seen.has(num)) return true;
+        seen.add(num);
+    }
+    return false; 
+};

two-sum/heesun-task.js

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+/*
+    Goal: return indices of the two numbers such that they add up to target
+
+    Plan:
+    - create a hash map (dict) to store number -> index
+    - loop through nums with index i
+        - get currentNum = nums[i]
+        - compute pairNum = target - currentNum
+        - if pairNum exists in dict
+            -> return [dict[pairNum], i]
+        - otherwise store currentNum in dict with its index
+    - if no pair is found, return [-1, -1]
+
+    space complexity: O(n)
+    time complexity: O(n)
+*/
+
+var twoSum = function(nums, target) {
+    const dict = {};
+
+    for (let i = 0; i < nums.length; i++) {
+        const currentNum = nums[i];
+        const pairNum = target - currentNum;
+
+        if (typeof dict[pairNum] === 'number') {
+            return [dict[pairNum], i];
+        } else {
+            dict[currentNum] = i;
+        }
+    }
+
+    return [-1, -1];
+};