Two Sum

Author: Sunjae95

two-sum/sunjae95.js

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+/**
+ * @description
+ * brainstorming:
+ * 1. O(n^2) brute force
+ * 2. hash table
+ */
+
+/**
+ * @description brainstorming 1 solve
+ * time complexity: O(n^2)
+ * space complexity: O(n)
+ */
+var twoSum = function (nums, target) {
+  for (let i = 0; i < nums.length; i++) {
+    for (let j = i + 1; j < nums.length; j++) {
+      if (nums[i] + nums[j] === target) return [i, j];
+    }
+  }
+};
+
+/**
+ * @description brainstorming 2 solve
+ * time complexity: O(n^2)
+ * space complexity: O(n)
+ */
+var twoSum = function (nums, target) {
+  const map = new Map();
+
+  nums.forEach((num, index) => {
+    if (!map.get(num)) return map.set(num, [index]);
+
+    map.set(num, map.get(num).concat(index));
+  });
+
+  for (let i = 0; i < nums.length; i++) {
+    const rest = target - nums[i];
+
+    if (!map.get(rest)) continue;
+
+    const indexList = map.get(rest);
+    for (let j = 0; j < indexList.length; j++) {
+      if (i === indexList[j]) continue;
+
+      return [i, indexList[j]];
+    }
+  }
+};