树的直径、最近公共祖先、树的变形

class Solution {
public:
    int treeDiameter(vector<vector<int>>& edges) {
        n = 0;
        for(vector<int>& edge : edges) {
            int x = edge[0];
            int y = edge[1];
            n = max(n, max(x, y));
        }
        n++;
        for(int i = 0; i < n; i++) to.push_back({});
        for(vector<int>& edge : edges) {
            int x = edge[0];
            int y = edge[1];
            to[x].push_back(y);
            to[y].push_back(x);
        }
        int p = findFarthest(0).first;
        return findFarthest(p).second;
    }
private:
    vector<vector<int>> to;
    int n;
    pair<int, int> findFarthest(int start) {
        vector<int> depth(n, -1);
        queue<int> q;
        q.push(start);
        depth[start] = 0;
        while(!q.empty()) {
            int x = q.front();
            q.pop();
            for (int y : to[x]) {
                if (depth[y] != -1) continue;
                depth[y] = depth[x] + 1;
                q.push(y);
            }
        }
        int ans = start;
        for(int i = 0; i < n; i++)
            if(depth[i] > depth[ans]) ans = i;
        return {ans, depth[ans]};
    }
};

/**
 * 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) {
        this->p=p;
        this->q=q;
        dfs(root);
        return ans;
    }
private:
    TreeNode* ans;
    TreeNode* p;
    TreeNode* q;
    pair<bool,bool> dfs(TreeNode* root){
        if(root==nullptr) return {false,false};
        pair<bool,bool> leftResult = dfs(root->left);
        pair<bool,bool> rightResult = dfs(root->right);
        pair<bool,bool> result;
        result.first = leftResult.first || rightResult.first || root==p;
        result.second = leftResult.second || rightResult.second || root==q;
        if(result.first && result.second && ans==nullptr) ans=root;
        return result;
    }
};