树的两个节点的最低公共祖先
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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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