Create lowest-common-ancestor-of-a-binary-tree-ii.cpp

Author: kamyu104

C++/lowest-common-ancestor-of-a-binary-tree-ii.cpp

@@ -0,0 +1,71 @@
+// Time:  O(n)
+// Space: O(h)
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
+        return iter_dfs(root, p, q);
+    }
+
+private:
+    TreeNode *iter_dfs(TreeNode* node, TreeNode* p, TreeNode* q) {
+        TreeNode *result = nullptr;
+        int ret = 0;
+        vector<tuple<int, TreeNode *, unique_ptr<int>, unique_ptr<int>, int*>> stk;
+        stk.emplace_back(1, node, nullptr,  nullptr, &ret);
+        while (!empty(stk)) {
+            const auto [step, node, ret1, ret2, ret] = move(stk.back()); stk.pop_back();
+            if (step == 1) {
+                if (!node) {
+                    continue;
+                }
+                auto ret1 = make_unique<int>(), ret2 = make_unique<int>();
+                auto p1 = ret1.get(), p2 = ret2.get();
+                stk.emplace_back(2, node, move(ret1), move(ret2), ret);
+                stk.emplace_back(1, node->right, nullptr, nullptr, p2);
+                stk.emplace_back(1, node->left, nullptr, nullptr, p1);
+            } else if (step == 2) {
+                auto curr = int(node == p || node == q);
+                if (curr + *ret1 + *ret2 == 2 && !result) {
+                    result = node;
+                }
+                *ret = curr + *ret1 + *ret2;
+            }
+        }
+        return result;
+    }
+};
+
+// Time:  O(n)
+// Space: O(h)
+class Solution2 {
+public:
+    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
+        TreeNode *result = nullptr;
+        dfs(root, p, q, &result);
+        return result;
+    }
+
+private:
+    int dfs(TreeNode* node, TreeNode* p, TreeNode* q, TreeNode** result) {
+        if (!node) {
+            return 0;
+        }
+        auto left = dfs(node->left, p, q, result);
+        auto right = dfs(node->right, p, q, result);
+        auto curr = int(node == p || node == q);
+        if (curr + left + right == 2 && !(*result)) {
+            *result = node;
+        }
+        return curr + left + right;
+    }
+};