Add 1644_Lowest_Common_Ancestor_of_a_Binary_Tree_II.java

seanprashad · Mar 25, 2021 · 22fd2a0 · 22fd2a0
1 parent b021672
commit 22fd2a0
Showing 1 changed file with 40 additions and 0 deletions.
diff --git a/Tree Depth First Search/1644_Lowest_Common_Ancestor_of_a_Binary_Tree_II.java b/Tree Depth First Search/1644_Lowest_Common_Ancestor_of_a_Binary_Tree_II.java
@@ -0,0 +1,40 @@
+class Solution {
+    private boolean pFound = false, qFound = false;
+
+    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+        TreeNode result = helper(root, p, q);
+
+        if (pFound && qFound && result != null) {
+            return result;
+        }
+        return null;
+    }
+
+    private TreeNode helper(TreeNode root, TreeNode p, TreeNode q) {
+        if (root == null) {
+            return null;
+        }
+
+        TreeNode left = helper(root.left, p, q);
+        TreeNode right = helper(root.right, p, q);
+
+        if (root == p) {
+            pFound = true;
+            return root;
+        }
+
+        if (root == q) {
+            qFound = true;
+            return root;
+        }
+
+        if (left == null) {
+            return right;
+        }
+        if (right == null) {
+            return left;
+        }
+
+        return root;
+    }
+}