product-of-array-except-self

Author: taewanseoul

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

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+/**
+ * 238. Product of Array Except Self
+ * Given an integer array nums, return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i].
+ * The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer.
+ * You must write an algorithm that runs in O(n) time and without using the division operation.
+ *
+ * https://leetcode.com/problems/product-of-array-except-self/description/
+ */
+
+// O(n) time
+// O(1) space
+function productExceptSelf(nums: number[]): number[] {
+  const result = new Array(nums.length).fill(1);
+
+  let left = 1;
+  for (let i = 0; i < nums.length - 1; i++) {
+    left *= nums[i];
+    result[i + 1] *= left;
+  }
+
+  let right = 1;
+  for (let i = nums.length - 1; i > 0; i--) {
+    right *= nums[i];
+    result[i - 1] *= right;
+  }
+
+  return result;
+}