LeetCode 0095 - Unique Binary Search Trees II

Unique Binary Search Trees II

Desicription

Given an integer n, generate all structurally unique BST’s (binary search trees) that store values 1…n.

For example, Given n = 3, your program should return all 5 unique BST’s shown below.

代码语言：javascript复制

1         3     3      2      1
        /     /      /       
  3     2     1      1   3      2
 /     /                        
2     1         2                 3

Solution

代码语言：javascript复制

/**
 * 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 {
private:
    vector<TreeNode*> searchTree(int left, int right) {
        vector<TreeNode*> res;
        if(left > right) {
            res.push_back(NULL);
            return res;
        }
        for(int i = left; i <= right; i  ) {
            vector<TreeNode*> leftVec = searchTree(left, i-1);
            vector<TreeNode*> rightVec = searchTree(i 1, right);
            for(int j = 0; j < leftVec.size(); j  ) {
                for(int k = 0; k < rightVec.size(); k  ) {
                    TreeNode* root = new TreeNode(i);
                    root->left = leftVec[j];
                    root->right = rightVec[k];
                    res.push_back(root);
                }
            }
        }
        return res;
    }
public:
    vector<TreeNode*> generateTrees(int n) {
        if(!n)
            return vector<TreeNode*>(0);
        return searchTree(1, n);
    }
};

binary return search store unique

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