Create steps-to-make-array-non-decreasing.py

Author: kamyu104

Python/steps-to-make-array-non-decreasing.py

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+# Time:  O(n)
+# Space: O(n)
+
+# mono stack, dp
+class Solution(object):
+    def totalSteps(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        dp = [0]*len(nums)  # dp[i]: number of rounds for a[i] to remove all the covered elements
+        stk = []
+        for i in reversed(xrange(len(nums))):
+            while stk and nums[stk[-1]] < nums[i]:
+                dp[i] = max(dp[i]+1, dp[stk.pop()])
+            stk.append(i)
+        return max(dp)
+
+
+# Time:  O(n)
+# Space: O(n)
+# mono stack, dp
+class Solution2(object):
+    def totalSteps(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        dp = [0]*len(nums)  # dp[i]: number of rounds for a[i] to be removed
+        stk = []
+        for i in xrange(len(nums)):
+            curr = 0
+            while stk and nums[stk[-1]] <= nums[i]:
+                curr = max(curr, dp[stk.pop()])
+            if stk:
+                dp[i] = curr+1
+            stk.append(i)
+        return max(dp)