Leetcode 236. Lowest Common Ancestor of a Binary Tree

triplebee

发布于 2018-01-12 14:43:30

5540

发布于 2018-01-12 14:43:30

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.

接235，找出二叉树上两个点的LCA，这次没有BST的性质可以使用了。

同样非常简单，只需要判断两个点是不是出现在二叉树的同一侧就行了。

/**
 * 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) return NULL;
        if(p == root || q == root) return root;
        TreeNode* l = lowestCommonAncestor(root->left, p, q);
        TreeNode* r = lowestCommonAncestor(root->right, p, q);
        if(!l) return r;
        else if(!r) return l;
        else return root;
        
    }
};

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原始发表：2017-04-06 ，如有侵权请联系 cloudcommunity@tencent.com 删除

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