Lowest Common Ancestor of a Binary Tree

最新推荐文章于 2024-10-16 01:06:12 发布

原创最新推荐文章于 2024-10-16 01:06:12 发布 · 314 阅读

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BST:

/**
 * 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) {
        if (!root) return NULL;
        int a = p->val < q->val ? p->val : q->val;
        int b = p->val > q->val ? p->val : q->val;
        if (a <= root->val && b >= root->val) {
            return root;
        }
        if (a < root->val && b < root->val) {
            return lowestCommonAncestor(root->left, p, q);
        }
        if (a > root->val && b > root->val) {
            return lowestCommonAncestor(root->right, p, q);
        }
    }
};

BT:

/**
 * 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:
    bool traverse(TreeNode* root, TreeNode *p, TreeNode *q, TreeNode *&res) {
        if (!root) return false;
        if (root == p && root == q) {
            res = root;
            return true;
        }
        
        bool f = false;
        if (root == p || root == q) {
            f = true;
        }
        
        bool fl = traverse(root->left, p, q, res);
        bool fr = traverse(root->right, p, q, res);
        
        if (!res && ((fl && fr) || (f && fl) || (f && fr))) {
            res = root;
            return true;
        } else {
            return (f || fl || fr);
        }
    }
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        TreeNode *res = NULL;
        traverse(root, p, q, res);
        return res;
        
    }
};