https://leetcode.com/problems/product-of-array-except-self/

interview_prep/algorithm/java/ide_handicapped/product_of_array_except_self/Solution.java

@@ -0,0 +1,57 @@
+import java.util.Arrays;
+
+class Solution {
+    /**
+     * 2n
+     */
+    public int[] productExceptSelf(int[] nums) {
+        int[] prefixProduct = new int[nums.length];
+        prefixProduct[0] = 1;
+        for (int i = 1; i < nums.length; i++) {
+            prefixProduct[i] = prefixProduct[i-1] * nums[i-1];
+        }
+
+        int suffixProduct = 1;
+        for (int i = nums.length-1; i >= 0; i--) {
+            prefixProduct[i] = prefixProduct[i] * suffixProduct;
+            suffixProduct = suffixProduct * nums[i];
+        }
+
+        return prefixProduct;
+    }
+
+    /**
+     * n^2
+     */
+    public int[] productExceptSelfNaive(int[] nums) {
+
+        int[] res = new int[nums.length];
+        Arrays.fill(res, 1);
+        for(int i =0; i< nums.length; i++){
+            for(int j = 0; j < nums.length; j++){
+                if(i!=j){
+                    res[j] = res[j] * nums[i];
+                }
+            }
+        }
+        return res;
+    }
+    public static void main(String[] args) {
+        //https://leetcode.com/problems/product-of-array-except-self/
+        Solution self = new Solution();// pretend to be python :v
+        assert Arrays.equals(
+            self.productExceptSelf(new int[]{1,2,3,4}),
+            new int[]{24,12,8,6}
+        );
+
+        assert Arrays.equals(
+            self.productExceptSelf(new int[]{-1,1,0,-3,3}),
+            new int[]{0,0,9,0,0}
+        );
+
+        assert Arrays.equals(
+            self.productExceptSelf(new int[]{2,3,4,5}),
+            new int[]{60,40, 30,24}
+        );
+    }
+}