solution of 238 product of array excep self

Author: grapefruit13

product-of-array-except-self/grapefruit13.ts

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+/**
+ * @description Return an array where each element is the product of all numbers in nums excep nums
+ * @param {number[]} nums
+ * @returns {number[]}
+ */
+function productExceptSelf(nums: number[]): number[] {
+  // result array (stores prefix products first)
+  const answer = new Array(nums.length);
+
+  // prefix product: product of all elements to the left of i
+  answer[0] = 1;
+  for (let i = 1; i < nums.length; i++) {
+    // multiply previous prefix with the previous number
+    answer[i] = answer[i - 1] * nums[i - 1];
+  }
+
+  // suffix product: product of all elements to the right of i
+  let rightProduct = 1;
+  for (let i = nums.length - 1; i >= 0; i--) {
+    // multiply prefix product and suffix product
+    answer[i] *= rightProduct;
+    // update suffix product for next iteration
+    rightProduct *= nums[i];
+  }
+
+  return answer;
+}