Update find-unique-binary-string.cpp

Author: kamyu104

C++/find-unique-binary-string.cpp

@@ -6,7 +6,82 @@ class Solution {
     string findDifferentBinaryString(vector<string>& nums) {
         string result;
         for (int i = 0; i < size(nums); ++i) {
-            result.push_back((nums[i][i] == '0') ? : '1' : '0');
+            result.push_back((nums[i][i] == '0') ? '1' : '0');
+        }
+        return result;
+    }
+};
+
+// Time:  O(k * n) = O(n^2), k is len(nums)
+//                         , n is len(nums[0])
+// Space: O(k) = O(n)
+class Solution2 {
+public:
+    string findDifferentBinaryString(vector<string>& nums) {
+        const int n = size(nums[0]);
+        unordered_set<int> lookup;
+        for (const auto& x : nums) {  // Time: O(k * n) = O(n^2)
+            lookup.emplace(to_decimal(x));
+        }
+        const int total = 1 << n;
+        for (int i = 0; i < total; ++i) {  // Time: O(k + n) = O(n)
+            if (!lookup.count(i)) {
+                return to_binary(i, n);
+            }
+        }
+        return "";
+    }
+
+private:
+    int to_decimal(const string& num) {  // Time: O(n)
+        return accumulate(cbegin(num), cend(num), 0,
+                          [](const auto& total, const auto& x) {
+                              return total * 2 + (x - '0');
+                          });
+    }
+    
+    string to_binary(int num, int n) {  // Time: O(n)
+        string result;
+        for (int basis = 1 << (n - 1); basis; basis >>= 1) {
+            result.push_back((num & basis) ? '1' : '0');
+        }
+        return result;
+    }
+};
+
+// Time:  O(k * n + n * 2^n) = O(n * 2^n), k is len(nums)
+//                                       , n is len(nums[0])
+// Space: O(k) = O(1) ~ O(2^n)
+class Solution_Extra {
+public:
+    vector<string> findAllDifferentBinaryStrings(vector<string>& nums) {
+        const int n = size(nums[0]);
+        unordered_set<int> lookup;
+        for (const auto& x : nums) {  // Time: O(k * n) = O(n * 2^n)
+            lookup.emplace(to_decimal(x));
+        }
+        vector<string> result;
+        const int total = 1 << n;
+        for (int i = 0; i < total; ++i) {  // Time: O(2^n + n * (2^n - k))
+            if (!lookup.count(i)) {
+                result.emplace_back(to_binary(i, n));
+            }
+        }
+        return result;
+    }
+
+private:
+    int to_decimal(const string& num) {  // Time: O(n)
+        return accumulate(cbegin(num), cend(num), 0,
+                          [](const auto& total, const auto& x) {
+                              return total * 2 + (x - '0');
+                          });
+    }
+    
+    string to_binary(int num, int n) {  // Time: O(n)
+        string result;
+        for (int basis = 1 << (n - 1); basis; basis >>= 1) {
+            result.push_back((num & basis) ? '1' : '0');
         }
         return result;
     }