Create can-i-win.cpp

Author: kamyu104

C++/can-i-win.cpp

@@ -0,0 +1,35 @@
+// Time:  O(n!)
+// Space: O(n)
+
+class Solution {
+public:
+    bool canIWin(int maxChoosableInteger, int desiredTotal) {
+        if ((1 + maxChoosableInteger) * (maxChoosableInteger / 2) < desiredTotal) {
+            return false;
+        }
+        unordered_map<int, int> lookup;
+        return canIWinHelper(maxChoosableInteger, desiredTotal, 0, &lookup);
+    }
+
+private:
+    int canIWinHelper(int maxChoosableInteger, int desiredTotal,
+                      int visited, unordered_map<int, int> *lookup) {
+
+        if  (lookup->find(visited) != lookup->end()) {
+            return (*lookup)[visited];
+        }
+        int mask = 1;
+        for (int i = 0; i < maxChoosableInteger; ++i) {
+            if (!(visited & mask)) {
+                if (i + 1 >= desiredTotal ||
+                    !canIWinHelper(maxChoosableInteger, desiredTotal - (i + 1), visited | mask, lookup)) {
+                    (*lookup)[visited] = true;
+                    return true;
+                }
+            }
+            mask <<= 1;
+        }
+        (*lookup)[visited] = false;
+        return false;
+    }
+};