Create paint-fence.py

Author: kamyu104

Python/paint-fence.py

@@ -0,0 +1,42 @@
+# Time:  O(n)
+# Space: O(1)
+
+# DP solution with rolling window.
+class Solution(object):
+    def numWays(self, n, k):
+        """
+        :type n: int
+        :type k: int
+        :rtype: int
+        """
+        if n == 0:
+            return 0
+        elif n == 1:
+            return k
+        ways = [0] * 3
+        ways[0] = k
+        ways[1] = (k - 1) * ways[0] + k
+        for i in xrange(2, n):
+            ways[i % 3] = (k - 1) * (ways[(i - 1) % 3] + ways[(i - 2) % 3])
+        return ways[(n - 1) % 3]
+
+# Time:  O(n)
+# Space: O(n)
+# DP solution.
+class Solution2(object):
+    def numWays(self, n, k):
+        """
+        :type n: int
+        :type k: int
+        :rtype: int
+        """
+        if n == 0:
+            return 0
+        elif n == 1:
+            return k
+        ways = [0] * n
+        ways[0] = k
+        ways[1] = (k - 1) * ways[0] + k
+        for i in xrange(2, n):
+            ways[i] = (k - 1) * (ways[i - 1] + ways[i - 2])
+        return ways[n - 1]