[数据结构与算法]654. 最大二叉树

题目链接

/**
 * 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:
    TreeNode* traver(vector<int> nums, int left, int right) {
        if (left >= right) return NULL;
        int maxIndex = left;
        for (int i = left+1; i < right; i++) {
            if (nums[i] > nums[maxIndex])
                maxIndex = i;
        }
        TreeNode* node = new TreeNode(nums[maxIndex]);
        node->left = traver(nums, left, maxIndex);
        node->right = traver(nums, maxIndex+1, right);
        return node;
    }
    TreeNode* constructMaximumBinaryTree(vector<int>& nums) {
        // 14
        int left = 0;
        int right = nums.size();
        return traver(nums, left, right);
    }
};

总结

• 采用先序遍历
• 左开右闭区间
• 找到最大值的下标maxIndex，构建根节点
• 递归构造左子树、右子树