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236.lowestCommonAncestor.cpp
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75 lines (66 loc) · 1.57 KB
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/*
@filename binary_tree/236.lowestCommonAncestor.cpp
@author caonan
@date 2023-09-09 14:30:23
@reference leetcode
@url https://leetcode.cn/problems/lowest-common-ancestor-of-a-binary-tree/
@brief
*/
#include <cassert>
#include <climits>
#include <cstdio>
#include <algorithm>
#include <bitset>
#include <deque>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <unordered_map>
#include <unordered_set>
#include <vector>
using namespace std;
struct TreeNode {
int val;
TreeNode* left;
TreeNode* right;
TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
};
class Solution {
public:
// 用额外空间来记录每个节点的父节点指针，从而找到公共祖先
TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
parent_map_[root] = nullptr;
dfs(root);
unordered_set<TreeNode*> path_history;
while (parent_map_.find(p) != parent_map_.end()) {
path_history.insert(p);
p = parent_map_[p];
}
while (parent_map_.find(q) != parent_map_.end()) {
if (path_history.find(q) != path_history.end()) {
return q;
}
q = parent_map_[q];
}
return nullptr;
}
void dfs(TreeNode* root) {
if (root == nullptr) {
return;
}
if (root->left) {
parent_map_[root->left] = root;
dfs(root->left);
}
if (root->right) {
parent_map_[root->right] = root;
dfs(root->right);
}
}
private:
unordered_map<TreeNode*, TreeNode*> parent_map_;
};
int main() { return 0; }