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.

/**
 * 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:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if(!root||p==root||q==root)
            return root;
        TreeNode * left =lowestCommonAncestor(root->left,p,q);
        TreeNode * right=lowestCommonAncestor(root->right,p,q);
        if(left&&right)//p和q分属root两边
            return root;
        return left? left:right;//p和q只是位于左右子树之中的一个
         
    }
};

236.Lowest Common Ancestor of a Binary Tree

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原文地址：http://www.cnblogs.com/zhoudayang/p/5041425.html