Create count-number-of-texts.py

Python/count-number-of-texts.py

@@ -0,0 +1,19 @@
+# Time:  O(n)
+# Space: O(1)
+
+# dp
+class Solution(object):
+    def countTexts(self, pressedKeys):
+        """
+        :type pressedKeys: str
+        :rtype: int
+        """
+        MOD = 10**9+7
+        dp = [1]*5
+        for i in xrange(1, len(pressedKeys)+1):
+            dp[i%5] = 0
+            for j in reversed(xrange(max(i-(4 if pressedKeys[i-1] in "79" else 3), 0), i)):
+                if pressedKeys[j] != pressedKeys[i-1]:
+                    break
+                dp[i%5] = (dp[i%5]+dp[j%5])%MOD
+        return dp[len(pressedKeys)%5]