LeetCode——Convert Sorted Array to Binary Search Tree

pickless

于 2013-09-22 00:41:46 发布

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分类专栏： Online Judge 文章标签： leetcode

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本文介绍了一种将有序数组转换为高度平衡二叉搜索树的方法。通过递归地选取中间元素作为根节点，并将左右子数组分别构建成左子树和右子树，确保了树的高度平衡。

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Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

» Solve this problem

每次对半分。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private:
    TreeNode *build(vector<int> &num, int l, int r) {
        TreeNode *root;
        if (l > r) {
            root = NULL;
        }
        else {
            int mid = (l + r) / 2;
            root = new TreeNode(num[mid]);
            root->left = build(num, l, mid - 1);
            root->right = build(num, mid + 1, r);
        }
        return root;
    }
    
public:
    TreeNode *sortedArrayToBST(vector<int> &num) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        return build(num, 0, num.size() - 1);
    }
};