Create maximum-number-of-achievable-transfer-requests.py

Author: kamyu104

Python/maximum-number-of-achievable-transfer-requests.py

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+# Time:  O((n + r) * 2^r)
+# Space: O(n + r)
+
+import itertools
+
+
+# early return solution
+class Solution(object):
+    def maximumRequests(self, n, requests):
+        """
+        :type n: int
+        :type requests: List[List[int]]
+        :rtype: int
+        """
+        for k in reversed(xrange(1, len(requests)+1)):
+            for c in itertools.combinations(xrange(len(requests)), k):
+                change = [0]*n
+                for i in c:
+                    change[requests[i][0]] -= 1
+                    change[requests[i][1]] += 1
+                if all(c == 0 for c in change):
+                    return k  # early return
+        return 0
+    
+
+# Time:  O((n + r) * 2^r)
+# Space: O(n + r)
+# full search solution (much slower)
+class Solution(object):
+    def maximumRequests(self, n, requests):
+        """
+        :type n: int
+        :type requests: List[List[int]]
+        :rtype: int
+        """
+        def evaluate(n, requests, mask):
+            change = [0]*n
+            base, count = 1, 0
+            for i in xrange(len(requests)):
+                if base & mask:
+                    change[requests[i][0]] -= 1
+                    change[requests[i][1]] += 1
+                    count += 1
+                base <<= 1
+            return count if all(c == 0 for c in change) else 0
+
+        return max(evaluate(n, requests, i) for i in xrange(1 << len(requests)))