Add week 3 solutions: product-of-array-except-self

Author: gitsunmin

product-of-array-except-self/gitsunmin.ts

@@ -0,0 +1,23 @@
+/**
+ * https://leetcode.com/problems/product-of-array-except-self
+ * time complexity : O(n)
+ * space complexity : O(1)
+ */
+function productExceptSelf(nums: number[]): number[] {
+    const n = nums.length;
+    const answer = new Array(n).fill(1);
+
+    let leftProduct = 1;
+    for (let i = 0; i < n; i++) {
+        answer[i] = leftProduct;
+        leftProduct *= nums[i];
+    }
+
+    let rightProduct = 1;
+    for (let i = n - 1; i >= 0; i--) {
+        answer[i] *= rightProduct;
+        rightProduct *= nums[i];
+    }
+
+    return answer;
+}