leetcode 日经贴，Cpp code -Lowest Common Ancestor of a Binary Search Tree

最新推荐文章于 2024-02-06 06:38:28 发布

bachelorchen

最新推荐文章于 2024-02-06 06:38:28 发布

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分类专栏：算法 Cpp leetcode

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本文探讨了在二叉搜索树中查找最近公共祖先的问题，详细介绍了两种不同的解决方案，包括递归方法和非递归方法。通过具体实例和代码实现，深入理解二叉搜索树的性质和最近公共祖先的查找逻辑。

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Lowest Common Ancestor of a Binary Search Tree

/**
 * 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) {
        matchcnt = 0;
        if (!root || !p || !q) {
            return NULL;
        }
        return lca(root, p, q);
    }
private:
    TreeNode* lca(TreeNode *r, TreeNode *p, TreeNode *q) {
        if (!r) {
            return NULL;
        }
        int a = matchcnt;
        TreeNode *ret = lca(r->left, p, q);
        if (ret) {
            return ret;
        }
        ret = lca(r->right, p, q);
        if (ret) {
            return ret;
        }
        if (r == p || r == q) {
            ++matchcnt;
        }
        if (a == 0 && matchcnt == 2) {
            return r;
        } 
        return NULL;
    }
    int matchcnt;
};

/**
 * 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 || !p || !q) {
            return NULL;
        }
        if (p->val > q->val) {
            swap(p, q);
        }
        return lca(root, p, q);
    }
private:
    TreeNode* lca(TreeNode *r, TreeNode *p, TreeNode *q) {
        if (!r) {
            return NULL;
        }
        if (r->val >= p->val && r->val <= q->val) {
            return r;
        }
        if (r->val < p->val) {
            return lca(r->right, p, q);
        } else {
            return lca(r->left, p, q);
        }
    }
};