LeetCode235:Lowest Common Ancestor of a Binary Search Tree
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.
二叉搜索樹的最低公共祖先節點。
因為二叉搜索樹的特性,即不論什麽一個節點的左子樹中的節點值都比該節點值小。不論什麽一個節點的右子樹中的節點值都比該節點值大。能夠依據這個特性在二叉樹中查找。
對於給定的兩個節點指針p和q,先調整p和q,使p指向值較小的那個節點。q指向值較大的那個節點;
然後從根節點node開始遍歷,假設q的值小於node的值,表示p和q都在node的左子樹中,更新node為node->left。
假設p的值大於node的值。表示p和q都在node的右子樹中,更新node為node->right;
否則表示找到的這個節點就是p和q的最低公共祖先節點。
runtime:40ms
/** * 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==NULL||p==NULL||q==NULL) return NULL; //使p保存值較小的節點。q保存值較大的節點 if(p->val > q->val) { /* TreeNode *tmp=p; p=q; q=tmp; */ //上面的代碼能夠直接寫成以下的樣子 swap(p,q); } TreeNode *result=root; while(true) { if(q->val < result->val) result=result->left; else if(p->val >result->val) result=result->right; else return result; } } };
LeetCode235:Lowest Common Ancestor of a Binary Search Tree