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Author: 10coder

FindCommonAnscestor.java

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+//https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/submissions/
+public class FindCommonAnscestor {
+
+    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+        //stores the common anscestor
+        TreeNode ans=new TreeNode();
+        findAncestor(root,p,q,ans);
+        return ans;
+    }
+
+    //Traverse the tree through dfs
+    // if the current node has either value check for children if they have other value if value found in either children or in this node this node is the ancestor
+
+    public boolean findAncestor(TreeNode r, TreeNode p, TreeNode q,TreeNode ans) {
+        if(r!=null) {
+            //check if this node has value
+            boolean centre=(r.val==p.val || r.val==q.val);
+            //check if one value is found in left subtree
+            boolean left=findAncestor(r.left,p,q,ans);
+            //check if one value is found in right subtree
+            boolean right=findAncestor(r.right,p,q,ans);
+
+            //if value found in either of 3 combinations set answer with this root value this condition is true only if this is the least common anscestor
+            if((centre && left) || (centre && right) || (left && right))
+                ans.val=r.val;
+            return (left || right || centre);
+        }
+        return false;
+    }
+}