654. Maximum Binary Tree

思路：正常遍历生成树结构即可
代码：

/**
 * 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 {
public:
    int getMaximumIndex(vector<int>& nums, int left, int right) {
        int index = left;
        for (int i = left; i <= right; i++) {
            if (nums[index] < nums[i]) index = i;
        }
        return index;
    }
    TreeNode* solution(vector<int>& nums, int i, int j) {
       if (i > j) return NULL;
        int index = getMaximumIndex(nums, i, j);
        TreeNode* root = new TreeNode(nums[index]);
        root -> left = solution(nums, i, index - 1);
        root -> right = solution(nums, index + 1, j);
        return root; 
    }
    TreeNode* constructMaximumBinaryTree(vector<int>& nums) {
        return solution(nums, 0, nums.size() - 1);
    }
};