654. Maximum Binary Tree(JAVA)

原題

Given an integer array with no duplicates. A maximum tree building on this array is defined as follow:
The root is the maximum number in the array.
The left subtree is the maximum tree constructed from left part subarray divided by the maximum number.
The right subtree is the maximum tree constructed from right part subarray divided by the maximum number.

Construct the maximum tree by the given array and output the root node of this tree.

Example 1:

Input: [3,2,1,6,0,5]
Output: return the tree root node representing the following tree:

6
/   \
3     5
\    /
2  0
\
1

Note:

The size of the given array will be in the range [1,1000].




解題思路

找出數組中最大的一個數，建立TreeNode，然後分別把最大的數的左邊的數字進行递歸，結果為TreeNode的左節點，右邊的數字的結果為右節點，即可。

代碼

import java.util.*;

class Solution {

    public TreeNode constructMaximumBinaryTree(int[] nums) {

        Vector<Integer> num = new Vector<Integer>();

        for (int i = 0; i < nums.length; i++) {

            num.add(nums[i]);

        }

        

        return loop(num);

    }

    

    TreeNode loop(Vector<Integer> nums) {

        if (nums.size() == 0) {

            return null;

        }

        

        int max = 0;

        for (int i = 0; i < nums.size(); i++) {

            if (nums.get(max) < nums.get(i)) {

                max = i;

            }

        }

        

        TreeNode root = new TreeNode(nums.get(max));

        Vector<Integer> left = new Vector<Integer>(), right = new Vector<Integer>();

        

        for (int i = 0; i < max; i++) {

            left.add(nums.get(i));

        }

        

        for (int i = max+1; i < nums.size(); i++) {

            right.add(nums.get(i));

        }

        

        root.left = loop(left);

        root.right = loop(right);

        

        return root;

    }

}

感想

Medium後面的題太難了，我都不會做了，還是做做前面簡單的吧QAQ