Add product-of-array-except-self solution in TypeScript

Author: Jeehay28

product-of-array-except-self/Jeehay28.ts

@@ -0,0 +1,65 @@
+// Approach 2
+// 🗓️ 2025-04-08
+// ⏳ Time Complexity: O(n + n + n) = O(n)
+// 💾 Space Complexity: O(1)
+// result: required output → not counted
+// before, after: two scalar variables → O(1)
+// So, the total extra space is O(1)
+
+function productExceptSelf(nums: number[]): number[] {
+  const result: number[] = new Array(nums.length).fill(1);
+  let before = 1;
+  let after = 1;
+
+  for (let i = 0; i < nums.length - 1; i++) {
+    before *= nums[i];
+    result[i + 1] *= before;
+  }
+
+  for (let i = nums.length - 1; i > 0; i--) {
+    after *= nums[i];
+    result[i - 1] *= after;
+  }
+  return result;
+}
+
+
+// Approach 1
+// 🗓️ 2025-04-08
+// ⏳ Time Complexity: O(n + n + n) = O(n)
+// 💾 Space Complexity: O(n + n) = O(n)
+
+// When we analyze space complexity,
+// we only count extra space used in addition to the input and required output.
+// ✅ before → O(n) extra
+// ✅ after → O(n) extra
+// 🚫 result is the output, so it’s not counted toward space complexity
+
+// function productExceptSelf(nums: number[]): number[] {
+//   // nums: an array of size n
+//   // before: nums[0], nums[1].., nums[i-2], nums[i-1]
+//   // after: nums[i+1], nums[i+2],..., nums[n-1]
+
+//   // input: [1, 2, 3, 4]
+//   // before: [1, 1, 2, 6]
+//   // after: [24, 12, 4, 1]
+//   // product: [24, 12, 8, 6]
+
+//   const before = new Array(nums.length).fill(1);
+//   const after = new Array(nums.length).fill(1);
+//   const result: number[] = [];
+
+//   for (let i = 0; i < nums.length - 1; i++) {
+//     before[i + 1] = before[i] * nums[i];
+//   }
+
+//   for (let i = nums.length - 1; i > 0; i--) {
+//     after[i - 1] = after[i] * nums[i];
+//   }
+
+//   for (let i = 0; i < nums.length; i++) {
+//     result[i] = before[i] * after[i];
+//   }
+
+//   return result;
+// }