Merge pull request liuyubobobo#16 from penpenps/master

Add py solutions for #0152 and #0169

0152-Maximum-Product-Subarray/py-0152/Solution1.py

@@ -0,0 +1,31 @@
+# Source : https://leetcode.com/problems/maximum-product-subarray/
+# Author : penpenps
+# Time   : 2019-07-21
+
+from typing import List
+
+# Travesal nums, use maxVal and minVal to keep max and min product end with current element
+# Time Complexity: O(n)
+# Space Complexity: O(1)
+
+class Solution:
+    def maxProduct(self, nums: List[int]) -> int:
+        n = len(nums)
+        minVal, maxVal = nums[0], nums[0]
+        ans = nums[0]
+        for i in range(1, n):
+            # If negative number, it should swap min and max for sign switching
+            if nums[i] < 0:
+                minVal, maxVal = maxVal, minVal
+            maxVal = max(nums[i]*maxVal, nums[i])
+            minVal = min(nums[i]*minVal, nums[i])
+            ans = max(maxVal, ans)
+
+        return ans
+
+
+if __name__ == '__main__':
+	s = Solution()
+	nums = [2,3,-2,4]
+	answer = s.maxProduct(nums)
+	print(answer)

0152-Maximum-Product-Subarray/py-0152/Solution2.py

@@ -0,0 +1,27 @@
+# Source : https://leetcode.com/problems/maximum-product-subarray/
+# Author : penpenps
+# Time   : 2019-07-21
+
+from typing import List
+
+# If even number of elements, the max product is multiple all nums together
+# If odd number, it should be divided into to part from one of the negative numbers and the answer is one of two seperated parts to multiple together
+# Time Complexity: O(n)
+# Space Complexity: O(1)
+
+class Solution:
+    def maxProduct(self, nums: List[int]) -> int:
+        n = len(nums)
+        rnums = nums[::-1]
+        for i in range(1, n):
+            nums[i] *= nums[i-1] or 1
+            rnums[i] *= rnums[i-1] or 1
+
+        return max(nums + rnums)
+
+
+if __name__ == '__main__':
+	s = Solution()
+	nums = [2,3,-2,4]
+	answer = s.maxProduct(nums)
+	print(answer)

0169-Majority-Element/py-0169/Solution.py

@@ -0,0 +1,13 @@
+# Source : https://leetcode.com/problems/majority-element/
+# Author : penpenps
+# Time   : 2019-07-22
+
+from typing import List
+
+# Sort nums and pick the (n/2)-th number
+# Time Complexity: O(nlogn)
+# Space Complexity: O(n)
+
+class Solution:
+    def majorityElement(self, nums: List[int]) -> int:
+        return sorted(nums)[len(nums)//2]

0169-Majority-Element/py-0169/Solution2.py

@@ -0,0 +1,18 @@
+# Source : https://leetcode.com/problems/majority-element/
+# Author : penpenps
+# Time   : 2019-07-22
+
+from typing import List
+
+# Count occurance for each number and find out the one whose occurance more than n/2 times
+# Time Complexity: O(n)
+# Space Complexity: O(n)
+
+import collections
+class Solution:
+    def majorityElement(self, nums: List[int]) -> int:
+        m = collections.Counter(nums)
+        n = len(nums)
+        for k,v in m.items():
+            if v >= n/2:
+                return k

0169-Majority-Element/py-0169/Solution3.py

@@ -0,0 +1,21 @@
+# Source : https://leetcode.com/problems/majority-element/
+# Author : penpenps
+# Time   : 2019-07-22
+
+from typing import List
+
+# Randomly pick one to check whether the answer
+# Time Complexity: Worst: O(infinity) Average: O(n)
+# Space Complexity: O(1)
+
+import random
+class Solution:
+    def majorityElement(self, nums: List[int]) -> int:
+        def occurance(nums, target):
+            return sum(1 if x == target else 0 for x in nums)
+
+        n = len(nums)
+        while True:
+            index = random.randint(0, n-1)
+            if occurance(nums, nums[index]) >= n / 2:
+                return nums[index]

0169-Majority-Element/py-0169/Solution4.py

@@ -0,0 +1,28 @@
+# Source : https://leetcode.com/problems/majority-element/
+# Author : penpenps
+# Time   : 2019-07-22
+
+from typing import List
+
+# Recursivly divide two half parts and search most occurance number
+# Time Complexity: O(nlogn)
+# Space Complexity: O(logn)
+
+class Solution:
+    def majorityElement(self, nums: List[int]) -> int:
+        def occurance(nums, left, right, target):
+            return sum(1 if x == target else 0 for x in nums[left:right+1])
+        def helper(nums, left, right):
+            length = right - left + 1
+            if length <= 2:
+                return nums[left]
+            mid = (left+right) // 2
+            leftMaj = helper(nums, left, mid)
+            rightMaj = helper(nums, mid+1, right)
+            if leftMaj == rightMaj:
+                return leftMaj
+            leftMajCnt = occurance(nums, left, mid, leftMaj)
+            rightMajCnt = occurance(nums, mid+1, right, rightMaj)
+
+            return leftMaj if leftMajCnt > rightMajCnt else rightMaj
+        return helper(nums, 0, len(nums)-1)

0169-Majority-Element/py-0169/Solution5.py

@@ -0,0 +1,23 @@
+# Source : https://leetcode.com/problems/majority-element/
+# Author : penpenps
+# Time   : 2019-07-22
+
+from typing import List
+
+# Boyer-Moore Voting Algorithm, count for one number, if not equal to current number, count minus 1 until ot 0 then try another number
+# Time Complexity: O(n)
+# Space Complexity: O(1)
+
+class Solution:
+    def majorityElement(self, nums: List[int]) -> int:
+        ans = nums[0]
+        count = 0
+        for n in nums:
+            if count == 0:
+                ans = n
+                count += 1
+            elif n == ans:
+                count += 1
+            else:
+                count -= 1
+        return ans

readme.md

@@ -185,7 +185,7 @@ email: [[email protected]](mailto:[email protected])
 | 149 | [Max Points on a Line](https://leetcode.com/problems/max-points-on-a-line/description/) | [solution](https://leetcode.com/problems/max-points-on-a-line/solution/) | [C++](0149-Max-Points-on-a-Line/cpp-0149/) | | |
 | 150 | [Evaluate Reverse Polish Notation](https://leetcode.com/problems/evaluate-reverse-polish-notation/description/) | [无] | [C++](0150-Evaluate-Reverse-Polish-Notation/cpp-0150/) | | |
 | 151 | [Reverse Words in a String](https://leetcode.com/problems/reverse-words-in-a-string/description/) | [无] | [C++](151-Reverse-Words-in-a-String/cpp-0151/) | | |
-| | | | | | |
+| 152 | [Maximum Product Subarray](https://leetcode.com/problems/maximum-product-subarray/) | [无] | | | [Python](0152-Maximum-Product-Subarray/py-0152/) |
 | 153 | [Find Minimum in Rotated Sorted Array](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array/description/) | [solution](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array/solution/) | [C++](0153-Find-Minimum-in-Rotated-Sorted-Array/cpp-0153/) | | |
 | | | | | | |
 | 155 | [Min Stack](https://leetcode.com/problems/min-stack/description/) | [无] | [C++](0155-Min-Stack/cpp-0155/) | | |
@@ -196,7 +196,7 @@ email: [[email protected]](mailto:[email protected])
 | | | | | | |
 | 167 | [Two Sum II - Input array is sorted](https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/description/) | [solution](https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/solution/) | [C++](0167-Two-Sum-II-Input-array-is-sorted/cpp-0167/) | [Java](0167-Two-Sum-II-Input-array-is-sorted/java-0167/src/) | |
 | | | | | | |
-| 169 | [Majority Element](https://leetcode.com/problems/majority-element/description/) | [solution](https://leetcode.com/problems/majority-element/solution/) | [C++](0169-Majority-Element/cpp-0169/) | | |
+| 169 | [Majority Element](https://leetcode.com/problems/majority-element/description/) | [solution](https://leetcode.com/problems/majority-element/solution/) | [C++](0169-Majority-Element/cpp-0169/) | | [Python](0169-Majority-Element/py-0169/) |
 | 170 | [Two Sum III - Data structure design](https://leetcode.com/problems/two-sum-iii-data-structure-design/description/) | [无] | [C++](0170-Two-Sum-III-Data-structure-design/cpp-0170/) | | |
 | 171 | [Excel Sheet Column Number](https://leetcode.com/problems/excel-sheet-column-number/description/) | [无] | [C++](0171-Excel-Sheet-Column-Number/cpp-0171/) | | |
 | | | | | | |