Create number-of-ways-to-select-buildings.py

Author: kamyu104

Python/number-of-ways-to-select-buildings.py

@@ -0,0 +1,18 @@
+# Time:  O(k * n) = O(n)
+# Space: O(k) = O(1)
+
+# dp
+class Solution(object):
+    def numberOfWays(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        K = 3
+        dp = [[0]*2 for _ in xrange(K)]  # dp[i][j]: number of ways of selecting i+1 buildings ending with type j
+        for c in s:
+            j = ord(c)-ord('0')
+            dp[0][j] += 1
+            for i in xrange(1, len(dp)):
+                dp[i][j] += dp[i-1][1^j]
+        return dp[-1][0]+dp[-1][1]