七月day26——二叉树

T1：leetcode.654 最大二叉树

/**
 * 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* traversal(vector<int>& nums, int left, int right) {
        if (left >= right) return nullptr;
        int maxValueIndex = left;
        for (int i = left   1; i < right; i  ) {
            if (nums[i] > nums[maxValueIndex]) maxValueIndex = i; 
        }
        TreeNode* root = new TreeNode(nums[maxValueIndex]);
        root->left = traversal(nums, left, maxValueIndex);
        root->right = traversal(nums, maxValueIndex   1, right);
        return root;
    }
    TreeNode* constructMaximumBinaryTree(vector<int>& nums) {
       return  traversal(nums, 0, nums.size());
    }
};
/*
1.traversal里有left right 不断更新边界 for循环里也需要更新
2.默认左开右闭
*/

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