238_Product_of_Array_Except_Self

Author: qiyuangong

README.md

@@ -87,6 +87,7 @@ Also, there are open source implementations for basic data structs and algorithm
 | 220 | [Contains Duplicate III](https://leetcode.com/problems/contains-duplicate-iii/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/220_Contains_Duplicate_III.py) | 1. Sort and binary Search <br>2. Bucket sort |
 | 221 | [Maximal Square](https://leetcode.com/problems/maximal-square/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/221_Maximal_Square.py) | 1. Brute force<br> 2. dp[i][j] = min(dp[i-1][j], dp[i-1][j-1], dp[i][j-1]) + 1, O(mn) and O(mn)<br>3. dp[j] = min([j], dp[j-1], prev) + 1, O(mn) and O(n)|
 | 228 | [Summary Ranges](https://leetcode.com/problems/summary-ranges/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/228_Summary_Ranges.py) | Detect start and jump, O(n) and O(1) |
+| 238 | [Product of Array Except Self](https://leetcode.com/problems/product-of-array-except-self/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/238_Product_of_Array_Except_Self.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/238_Product_of_Array_Except_Self.java) | The ans is [0,i -1] * [i+1, len- 1]. We can twice for left and right (reverse), O(n) and O(n) |
 | 243 | [Shortest Word Distance](https://leetcode.com/problems/shortest-word-distance/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/243_Shortest_Word_Distance.py) | Update index1 and index2, and check distance, O(n) and O(1) |
 | 246 | [Strobogrammatic Number](https://leetcode.com/problems/strobogrammatic-number/) &hearts; | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/246_Strobogrammatic_Number.py) | Hash table and reverse string, O(n) and O(n) |
 | 249 | [Group Shifted Strings](https://leetcode.com/problems/group-shifted-strings/) &hearts; | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/249_Group_Shifted_Strings.py) | Hash and generate hash code for each string, O(n) and O(n) |

java/238_Product_of_Array_Except_Self.java

@@ -0,0 +1,18 @@
+public class Solution {
+    public int[] productExceptSelf(int[] nums) {
+        int n = nums.length;
+        int[] res = new int[n];
+        res[0] = 1;
+        for (int i = 1; i < n; i++) {
+            // left part
+            res[i] = res[i - 1] * nums[i - 1];
+        }
+        int right = 1;
+        for (int i = n - 1; i >= 0; i--) {
+            res[i] *= right;
+            // right part
+            right *= nums[i];
+        }
+        return res;
+    }
+}

python/238_Product_of_Array_Except_Self.py

@@ -0,0 +1,14 @@
+class Solution(object):
+    def productExceptSelf(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: List[int]
+        """
+        ans = [1] * len(nums)
+        for i in range(1, len(nums)):
+            ans[i] = ans[i - 1] * nums[i - 1]
+        right = 1
+        for i in range(len(nums) - 1, -1, -1):
+            ans[i] *= right
+            right *= nums[i]
+        return ans