235. Lowest Common Ancestor of a Binary Search Tree
2017-02-23 23:38
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题目
Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.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).”
_______6______ / \ ___2__ ___8__
/ \ / \
0 _4 7 9
/ \
3 5
For example, the lowest common ancestor (LCA) of nodes 2 and 8 is 6. Another example is LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.
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思路
递归,两个节点最小的祖先就是最上面的公共根节点代码
#include <set> using namespace std; /** * 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(p->val > root->val && q->val > root->val) { return lowestCommonAncestor(root->right,p,q); } if(p->val < root->val && q->val < root->val) { return lowestCommonAncestor(root->left,p,q); } return root; } };
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