654.cpp

/**
 * 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:
    TreeNode* constructMaximumBinaryTree(vector<int>& nums) {
        return build(0, nums.size() - 1, nums);
    }
    TreeNode* build(int l, int r, vector<int>& nums) {
        if (l > r) return NULL;
        int idx = l;
        for(int i = l + 1; i <= r; i++)
            if (nums[i] > nums[idx]) idx = i;
        TreeNode* root = new TreeNode(nums[idx]);
        root->left = build(l, idx - 1, nums);
        root->right = build(idx + 1, r, nums);
        return root;
    }
};