最低公共祖先Lowest Common Ancestor of a Binary Tree

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.

解：

/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
//采用先序遍历算法实现查找最低公共祖先
TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
if(root==NULL)
return NULL;
if(root==p || root==q) return root;

TreeNode * left=lowestCommonAncestor(root->left, p, q);
TreeNode * right=lowestCommonAncestor(root->right, p, q);
if(left && right)
return root;
return left?left:right;
}
};