product of array except self 완료

- time complexitiy: O(n)
- space complexitiy: O(1)

Author: highballplz

product-of-array-except-self/highball.js

@@ -0,0 +1,56 @@
+/* -------------------------------------------------------------------------- */
+/*              time complexitiy: O(n),  space complexitiy: O(n)              */
+/* -------------------------------------------------------------------------- */
+
+// const productExceptSelf = function (nums) {
+//   const result = [];
+//   const n = nums.length;
+
+//   if (n < 2) return result;
+
+//   const left = [1];
+//   const right = [1];
+
+//   for (let i = 1; i < n; i++) {
+//     left[i] = left[i - 1] * nums[i - 1];
+//   }
+
+//   for (let i = 1; i < n; i++) {
+//     right[i] = right[i - 1] * nums[n - i];
+//   }
+
+//   for (let i = 0; i < n; i++) {
+//     result[i] = left[i] * right[n - 1 - i];
+//     if (result[i] === 0) result[i] = Math.abs(result[i]); //0이 -0으로 표시되는 이슈 핸들
+//   }
+
+//   return result;
+// };
+
+/* -------------------------------------------------------------------------- */
+/*              time complexitiy: O(n),  space complexitiy: O(1)              */
+/* -------------------------------------------------------------------------- */
+
+const productExceptSelf = function (nums) {
+  const result = [1];
+  const n = nums.length;
+
+  if (n < 2) return result;
+
+  let prefix = 1;
+  let postfix = 1;
+
+  for (let i = 1; i < n; i++) {
+    prefix *= nums[i - 1];
+    result[i] = prefix;
+    if (i === n - 1 && result[i] === 0) result[i] = Math.abs(result[i]); //0이 -0으로 표시되는 이슈 핸들
+  }
+
+  for (let i = n - 2; i >= 0; i--) {
+    postfix *= nums[i + 1];
+    result[i] *= postfix;
+    if (result[i] === 0) result[i] = Math.abs(result[i]); //0이 -0으로 표시되는 이슈 핸들
+  }
+
+  return result;
+};