add lca

Author: tg123

lowest-common-ancestor-of-a-binary-tree/README.md

@@ -0,0 +1,57 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+public class Solution {
+
+    TreeNode lca;
+
+    TreeNode other;
+
+    boolean containOther(TreeNode root){
+
+        if(root == null) return false;
+
+        if(root == other) return true;
+
+        return containOther(root.left) || containOther(root.right);
+    }
+
+    void inorder(TreeNode root, TreeNode p, TreeNode q){
+        if(lca != null) return;
+
+        if(root == null) return;
+
+        if(other == null) inorder(root.left,  p, q);
+
+        if(other == null){
+            if(root == p){
+                other = q;
+            } else if (root == q){
+                other = p;
+            }
+        }
+
+        if(other != null){
+            // left contain one, need other
+            if(root == other || containOther(root.right)){
+                lca = root;
+            }
+        }
+
+        if(other == null) inorder(root.right, p, q);
+    }
+
+
+    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+        // a bit ugly
+        inorder(root, p, q);
+
+        return lca;
+    }
+}

lowest-common-ancestor-of-a-binary-tree/Solution.java

@@ -0,0 +1,7 @@
+---
+layout: solution
+title: Lowest Common Ancestor of a Binary Tree
+date: 2015-07-26 16:03:27+08:00
+leetcode_id: 236
+---
+{% include_relative README.md %}