Create count-the-number-of-winning-sequences.py

Author: kamyu104

Python/count-the-number-of-winning-sequences.py

@@ -0,0 +1,32 @@
+# Time:  O(n^2)
+# Space: O(n)
+
+import collections
+
+
+# dp
+class Solution(object):
+    def countWinningSequences(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        MOD = 10**9+7
+        lookup = {x:i for i, x in enumerate("FWE")}
+        dp = [collections.defaultdict(int) for _ in xrange(3)]
+        for i, c in enumerate(s):
+            new_dp = [collections.defaultdict(int) for _ in xrange(3)]
+            x = lookup[c]
+            for j in xrange(3):
+                diff = (j-x+1)%3-1
+                if i == 0:
+                    new_dp[j][diff] = 1
+                    continue
+                for k in xrange(3):
+                    if k == j:
+                        continue
+                    for v, c in dp[k].iteritems():
+                        new_dp[j][v+diff] = (new_dp[j][v+diff]+c)%MOD
+            dp = new_dp
+        return reduce(lambda accu, x: (accu+x)%MOD, (c for j in xrange(3) for v, c in dp[j].iteritems() if v >= 1), 0)
+