628_Maximum_Product_of_Three_Numbers

Author: qiyuangong

README.md

@@ -152,6 +152,7 @@ Also, there are open source implementations for basic data structs and algorithm
 | 572 | [Subtree of Another Tree](https://leetcode.com/problems/subtree-of-another-tree/description/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/572_Subtree_of_Another_Tree.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/572_Subtree_of_Another_Tree.java) | 1. Tree traverse and compare<br>2. Tree to string and compare |
 | 581 | [Shortest Unsorted Continuous Subarray](https://leetcode.com/problems/subtree-of-another-tree/description/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/581_Shortest_Unsorted_Continuous_Subarray.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/581_Shortest_Unsorted_Continuous_Subarray.java) | 1. Sort and find the difference (min and max), O(nlgn)<br>2. Using stack to find boundaries (push when correct order, pop when not correct), O(n) and O(n)<br>3. Find min and max of unordered array, O(n) and O(1)|
 | 617 | [Merge Two Binary Trees](https://leetcode.com/problems/merge-two-binary-trees/description/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/617_Merge_Two_Binary_Trees.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/617_Merge_Two_Binary_Trees.java) | Traverse both trees Recursion & Iterative (stack) |
+| 628 | [Maximum Product of Three Numbers](https://leetcode.com/problems/maximum-product-of-three-numbers/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/628_Maximum_Product_of_Three_Numbers.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/628_Maximum_Product_of_Three_Numbers.java) | Actually, we should only care about min1, min2 and max1-max3, to find these five elements, we can use 1. Brute force, O(n^3) and O(1)<br>2. Sort, O(nlogn) and O(1)<br>3. Single scan with 5 elements keep, O(n) and O(1) |
 | 654 | [Maximum Binary Tree](https://leetcode.com/problems/maximum-binary-tree/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/654_Maximum_Binary_Tree.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/654_Maximum_Binary_Tree.java) | 1. Divide and conquer, recursive, O(n^2)<br>2. Monotonic stack, O(n) |
 | 680 | [Valid Palindrome II](https://leetcode.com/problems/valid-palindrome-ii/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/680_Valid_Palindrome_II.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/680_Valid_Palindrome_II.java) | Recursively check s[left == end, when not equal delete left or right. |
 | 692 | [Top K Frequent Words](https://leetcode.com/problems/top-k-frequent-words/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/692_Top_K_Frequent_Words.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/692_Top_K_Frequent_Words.java) | 1. Sort based on frequency and alphabetical order, O(nlgn) and O(n)<br>2. Find top k with Heap, O(nlogk) and O(n) |

java/628_Maximum_Product_of_Three_Numbers.java

@@ -0,0 +1,31 @@
+public class Solution {
+    /*public int maximumProduct(int[] nums) {
+        Arrays.sort(nums);
+        return Math.max(nums[0] * nums[1] * nums[nums.length - 1], nums[nums.length - 1] * nums[nums.length - 2] * nums[nums.length - 3]);
+    }*/
+    
+    public int maximumProduct(int[] nums) {
+        int min1 = Integer.MAX_VALUE, min2 = Integer.MAX_VALUE;
+        int max1 = Integer.MIN_VALUE, max2 = Integer.MIN_VALUE, max3 = Integer.MIN_VALUE;
+        for (int n: nums) {
+            if (n <= min1) {
+                min2 = min1;
+                min1 = n;
+            } else if (n <= min2) {     // n lies between min1 and min2
+                min2 = n;
+            }
+            if (n >= max1) {            // n is greater than max1, max2 and max3
+                max3 = max2;
+                max2 = max1;
+                max1 = n;
+            } else if (n >= max2) {     // n lies betweeen max1 and max2
+                max3 = max2;
+                max2 = n;
+            } else if (n >= max3) {     // n lies betwen max2 and max3
+                max3 = n;
+            }
+        }
+        return Math.max(min1 * min2 * max1, max1 * max2 * max3);
+    }
+}
+

python/628_Maximum_Product_of_Three_Numbers.py

@@ -0,0 +1,30 @@
+class Solution(object):
+    # def maximumProduct(self, nums):
+    #     """
+    #     :type nums: List[int]
+    #     :rtype: int
+    #     """
+    #     nums.sort()
+    #     # Check min1*min2*max1 and max1*max2*max3
+    #     return max(reduce(lambda x, y: x * y, nums[:2]) * nums[-1],
+    #                reduce(lambda x, y: x * y, nums[-3:]))
+
+    def maximumProduct(self, nums):
+        min1 = min2 = float('inf')
+        max1 = max2 = max3 = float('-inf')
+        for num in nums:
+            if num <= min1:
+                min2 = min1
+                min1 = num
+            elif num <= min2:
+                min2 = num
+            if num >= max1:
+                max3 = max2
+                max2 = max1
+                max1 = num
+            elif num >= max2:
+                max3 = max2
+                max2 = num
+            elif num >= max3:
+                max3 = num
+        return max(min1 * min2 * max1, max1 * max2 * max3)