Create longest-mountain-in-array.py

Python/longest-mountain-in-array.py

@@ -0,0 +1,51 @@
+# Time:  O(n)
+# Space: O(1)
+
+# Let's call any (contiguous) subarray B (of A) a mountain
+# if the following properties hold:
+#
+# B.length >= 3
+# There exists some 0 < i < B.length - 1
+# such that B[0] < B[1] < ... B[i-1] < B[i] > B[i+1] > ... > B[B.length - 1]
+# (Note that B could be any subarray of A, including the entire array A.)
+#
+# Given an array A of integers, return the length of the longest mountain.
+#
+# Return 0 if there is no mountain.
+#
+# Example 1:
+#
+# Input: [2,1,4,7,3,2,5]
+# Output: 5
+# Explanation: The largest mountain is [1,4,7,3,2] which has length 5.
+# Example 2:
+#
+# Input: [2,2,2]
+# Output: 0
+# Explanation: There is no mountain.
+#
+# Note:
+# - 0 <= A.length <= 10000
+# - 0 <= A[i] <= 10000
+
+try:
+    xrange          # Python 2
+except NameError:
+    xrange = range  # Python 3
+
+
+class Solution(object):
+    def longestMountain(self, A):
+        """
+        :type A: List[int]
+        :rtype: int
+        """
+        result, up_len, down_len = 0, 0, 0
+        for i in xrange(1, len(A)):
+            if (down_len and A[i-1] < A[i]) or A[i-1] == A[i]:
+                up_len, down_len = 0, 0
+            up_len += A[i-1] < A[i]
+            down_len += A[i-1] > A[i]
+            if up_len and down_len:
+                result = max(result, up_len+down_len+1)
+        return result