653.-two-sum-iv-input-is-a-bst.md

653. Two Sum IV - Input is a BST

/**
 * 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) {
        if (!root) return false;
        unordered_set<int> st;
        queue<TreeNode*> q{{root}};
        while (!q.empty()) {
            auto t = q.front(); q.pop();
            if (st.count(k - t->val)) return true;
            st.insert(t->val);
            if (t->left) q.push(t->left);
            if (t->right) q.push(t->right);
        }
        return false;
    }
};