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).”
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.
方法一
递归
TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
if (!root || root == p || root == q) return root;
TreeNode* left = lowestCommonAncestor(root->left, p, q);
TreeNode* right = lowestCommonAncestor(root->right, p, q);
return !left ? right : !right ? left : root;
}
方法二
深度搜索
class Solution {
public:
TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
vector<TreeNode*> pp, pq;
dfs(root, p, pp);
dfs(root, q, pq);
TreeNode* result = nullptr;
int n = (int)std::min(pp.size(), pq.size());
for (int i = 0; i < n; i++){
if (pp[i] == pq[i])
result = pp[i];
else
break;
}
return result;
}
bool dfs(TreeNode* root, TreeNode* p, vector<TreeNode*>& pp) {
if (!root)
return false;
pp.push_back(root);
if (root == p || dfs(root->left, p, pp) || dfs(root->right, p, pp))
return true;
pp.pop_back();
return false;
}
};
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时间: 2024-10-08 08:27:32