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程式語言 - LeetCode - C++ - 653. Two Sum IV - Input is a BST

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題目：


解答：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    bool findTarget(TreeNode* root, int k) {
        unordered_set<int> st;

        auto dfs = [&](this auto&& dfs, TreeNode* n, int v) -> bool {
            if (!n) {
                return false;
            }

            if (st.count(v - n->val)) {
                return true;
            }

            st.insert(n->val);
            return dfs(n->left, v) | dfs(n->right, v);
        };

        return dfs(root, k);
    }
};