cpp: add «1609. Even Odd Tree»

Signed-off-by: Matej Focko <mfocko@redhat.com>

cpp/even-odd-tree.cpp

@@ -0,0 +1,49 @@
+#include <unordered_map>
+
+#ifdef _MF_TEST
+struct TreeNode {
+    int val;
+    TreeNode *left;
+    TreeNode *right;
+    TreeNode() : val(0), left(nullptr), right(nullptr) {}
+    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+    TreeNode(int x, TreeNode *left, TreeNode *right)
+        : val(x), left(left), right(right) {}
+};
+#endif
+
+class Solution {
+    auto isEvenOddTree(std::unordered_map<int, int> &view, int level,
+                       TreeNode *root) const -> bool {
+        if (root == nullptr) {
+            return true;
+        }
+
+        // check the parity
+        if (level % 2 == root->val % 2) {
+            return false;
+        }
+
+        // check the ordering
+        auto &last = view[level];
+        if (last != 0 && level % 2 == 0 && root->val <= last) {
+            return false;
+        } else if (last != 0 && level % 2 != 0 && root->val >= last) {
+            return false;
+        }
+        last = root->val;
+
+        if (!isEvenOddTree(view, level + 1, root->left) ||
+            !isEvenOddTree(view, level + 1, root->right)) {
+            return false;
+        }
+
+        return true;
+    }
+
+  public:
+    bool isEvenOddTree(TreeNode *root) const {
+        std::unordered_map<int, int> leftview;
+        return isEvenOddTree(leftview, 0, root);
+    }
+};