product Except self solution

Author: wad-jangjaejeong

product-of-array-except-self/jaejeong1.java

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+class SolutionProductExceptSelf {
+
+  public int[] productExceptSelf(int[] nums) {
+    // answer[i] = nums[0] * nums[1] * ... * nums[i-1] * nums[i+1] * ... * nums[n-1]
+    // answer[i] = left[i] * right[i]
+    // left[i] = nums[0] * nums[1] * ... * nums[i-1]
+    // right[i] = nums[i+1] * ... * nums[n-1]
+    // left[i] = left[i-1] * nums[i-1]
+    // right[i] = right[i+1] * nums[i+1]
+    // answer[i] = left[i] * right[i]
+    // 시간복잡도: O(N), 공간복잡도: O(N)
+    int n = nums.length;
+    int[] left = new int[n];
+    int[] right = new int[n];
+    int[] answer = new int[n];
+
+    left[0] = 1;
+    right[n - 1] = 1;
+
+    for (int i = 1; i < n; i++) {
+      left[i] = left[i - 1] * nums[i - 1];
+    }
+
+    for (int i = n - 2; i >= 0; i--) {
+      right[i] = right[i + 1] * nums[i + 1];
+    }
+
+    for (int i = 0; i < n; i++) {
+      answer[i] = left[i] * right[i];
+    }
+
+    return answer;
+  }
+}