Create construct-the-lexicographically-largest-valid-sequence.cpp

Author: kamyu104

C++/construct-the-lexicographically-largest-valid-sequence.cpp

@@ -0,0 +1,35 @@
+// Time:  O(n!)
+// Space: O(n)
+
+class Solution {
+public:
+    vector<int> constructDistancedSequence(int n) {
+        vector<int> result(2 * n - 1);
+        vector<bool> lookup(n + 1);
+        backtracking(n, 0, &lookup, &result);
+        return result;
+    }
+
+private:
+    bool backtracking(int n, int i, vector<bool> *lookup, vector<int> *result) {
+        if (i == size(*result)) {
+            return true;
+        }
+        if ((*result)[i]) {
+            return backtracking(n, i + 1, lookup, result);
+        }
+        for (int x = n; x >= 1; --x) {
+            int j = (x == 1) ? i : i + x;
+            if ((*lookup)[x] || j >= size(*result) || (*result)[j]) {
+                continue;
+            }
+            (*result)[i] = (*result)[j] = x, (*lookup)[x] = true;
+            if (backtracking(n, i + 1, lookup, result)) {
+                return true;
+            }
+            (*result)[i] = (*result)[j] = 0, (*lookup)[x] = false;
+            
+        }
+        return false;
+    }
+};