236. Lowest Common Ancestor of a Binary Tree Java solutions

Given a binary tree, find the lowest common ancestor (LCA) of the Given nodes in the tree.

According to the definition of the LCA in Wikipedia: "The lowest common ancestor is defined between," nodes V and W as the L Owest node in T, have both V and W as descendants (where we allow a node to be a descendant of itself). "

        _______3______       /                  ___5__          ___1__   /      \        /         6      _2       0       8         /           7   4

For example, the lowest common ancestor (LCA) of nodes and are 5 1 3 . Another example is LCA of nodes 5 4 5 and are, since a node can be a descendant of itself according to the L CA definition.

The parent dictionary of the node is established, and the P and Q are traversed forward respectively.

1 /**2 * Definition for a binary tree node.3 * public class TreeNode {4 * int val;5 * TreeNode left;6 * TreeNode right;7 * TreeNode (int x) {val = x;}8  * }9  */Ten  Public classSolution { One      PublicTreeNode lowestcommonancestor (TreeNode root, TreeNode p, TreeNode q) { Amap<treenode,treenode> parent =NewHashmap<treenode,treenode>(); -deque<treenode> s =NewArraydeque<treenode>(); -Parent.put (Root,NULL); the S.add (root); -          while(!parent.containskey (P) | |!Parent.containskey (q)) { -TreeNode n =S.pop (); -             if(N.left! =NULL){ + Parent.put (n.left,n); - S.add (n.left); +             } A             if(N.right! =NULL){ at Parent.put (n.right,n); - S.add (n.right); -             } -         } -Set<treenode> set =NewHashset<treenode>(); -          while(p!=NULL){ in Set.add (p); -p =Parent.get (p); to         } +          while(!set.contains (q)) Q =Parent.get (q); -         returnQ; the     } *}

236. Lowest Common Ancestor of a Binary Tree Java solutions