js16-leetcode-1-two-sum-optimized

Author: mzeeshan138

js16-leetcode-1-two-sum-optimized.js

@@ -0,0 +1,28 @@
+/**
+ * @param {number[]} nums
+ * @param {number} target
+ * @return {number[]}
+ */
+var twoSum = function (nums, target) {
+  // Map from number → its index in nums
+  const seen = new Map();
+
+  for (let i = 0; i < nums.length; i++) {
+    const complement = target - nums[i];
+    // Have we already seen the complement?
+    if (seen.has(complement)) {
+      // Yes: return [index of complement, current index]
+      return [seen.get(complement), i];
+    }
+    // Otherwise, record this number and its index
+    seen.set(nums[i], i);
+  }
+
+  // Problem guarantees exactly one solution, so we should never reach here
+  return [];
+};
+
+console.log(twoSum([2, 7, 11, 15], 9)); //[0,1]
+console.log(twoSum([3, 2, 4], 6)); //[1,2]
+
+//overall time is O(n), with O(n) extra space for the map