Create sum-of-subarray-ranges.py

Author: kamyu104

Python/sum-of-subarray-ranges.py

@@ -0,0 +1,27 @@
+# Time:  O(n)
+# Space: O(n)
+
+class Solution(object):
+    def subArrayRanges(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        result = 0
+        stk = []
+        for i in xrange(len(nums)+1):
+            x = nums[i] if i < len(nums) else float("inf")
+            while stk and nums[stk[-1]] <= x:
+                j = stk.pop()
+                k = stk[-1] if stk else -1
+                result += nums[j]*(j-k)*(i-j)
+            stk.append(i)
+        stk = []
+        for i in xrange(len(nums)+1):
+            x = nums[i] if i < len(nums) else float("-inf")
+            while stk and nums[stk[-1]] >= x:
+                j = stk.pop()
+                k = stk[-1] if stk else -1
+                result -= nums[j]*(j-k)*(i-j)
+            stk.append(i)
+        return result