add: #239 Product of Array Except Self

Author: sukyoungshin

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

@@ -0,0 +1,48 @@
+// 1번 풀이
+function productExceptSelf1(nums: number[]): number[] {
+  const result: number[] = new Array(nums.length).fill(1);
+
+  applyLeftProducts(nums, result);
+  applyRightProducts(nums, result);
+
+  return result;
+};
+
+function applyLeftProducts(nums: number[], result: number[]) {
+  let prefix = 1;
+  for (let i = 0; i < nums.length; i++) {
+    result[i] = prefix;
+    prefix *= nums[i];
+  }
+};
+
+function applyRightProducts(nums: number[], result: number[]) {
+  let suffix = 1;
+  for (let i = nums.length - 1; i >= 0; i--) {
+    result[i] *= suffix;
+    suffix *= nums[i];
+  }
+};
+
+// 2번 풀이
+function productExceptSelf2(nums: number[]): number[] {
+    const length = nums.length;
+    const result: number[] = new Array(length).fill(1);
+  
+    // 1단계: 왼쪽 누적 곱 저장
+    let prefix = 1;
+    for (let i = 0; i < length; i++) {
+      result[i] = prefix;
+      prefix *= nums[i];
+    }
+  
+    // 2단계: 오른쪽 누적 곱 곱하기 (in-place)
+    let suffix = 1;
+    for (let i = length - 1; i >= 0; i--) {
+      result[i] *= suffix;
+      suffix *= nums[i];
+    }
+  
+    return result;
+  }
+