c_cpp 236.二叉树的最低共同祖先 - 难度中等 - 2018.9.13

Posted 2021-05-14

//递归法：
class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if (root == p || root == q || root == NULL) {
            return root;
        }
        TreeNode *l = lowestCommonAncestor(root->left, p, q);
        TreeNode *r = lowestCommonAncestor(root->right, p, q);
        if (l && r) {
            return root;
        }
        return l ? l : r;
    }
};

//递归找寻节点，匹配最长公共路径：
class Solution {
public:
    // 找寻路径数组
    bool dfs(TreeNode* root, TreeNode *t, vector<TreeNode *>& tV) {
        if (root == NULL) {
            return false;
        }
        tV.push_back(root);
        if (root == t) {
            return true;
        }
        if (dfs(root->left, t, tV)) {
            return true;
        }
        if (dfs(root->right, t, tV)) {
            return true;
        }
        tV.pop_back();
        return false;
    }
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        vector <TreeNode *> pDFSVec;
        dfs(root, p, pDFSVec);
        vector <TreeNode *> qDFSVec;
        dfs(root, q, qDFSVec);
        TreeNode *re;
        // 匹配公共节点
        for (int i = 0; i < min(pDFSVec.size(), qDFSVec.size()); i++) {
            if (pDFSVec[i] != qDFSVec[i]) {
                break;
            }
            re = pDFSVec[i];
        }
        return re;
    }
};