[leetcode] 236. Lowest Common Ancestor of a Binary Tree

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

According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has 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 5 and 1 is 3. Another example is LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.

Solution:

一个节点root，只有左子树中有p或q之一，AND 右子树中有p或q之一。

在root的左右分支寻找p或q。

 1 TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) 
 2     {
 3         if (root == NULL || root == p || root == q)
 4             return root;
 5             
 6         TreeNode* left = lowestCommonAncestor(root->left, p, q);
 7         TreeNode* right = lowestCommonAncestor(root->right, p, q);
 8         
 9         if (left && right)
10             return root;
11         return left ? left : right;
12     }

[leetcode] 236. Lowest Common Ancestor of a Binary Tree

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原文地址：http://www.cnblogs.com/ym65536/p/5460480.html