[Leetcode] 654. Maximum Binary Tree maximum Binary Tree

Given an integer array with no duplicates. A maximum tree building on this array is defined as follow:

1. The root is the maximum number in the array.
2. The left subtree is the maximum tree constructed from left part subarray divided by the maximum number.
3. 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:

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

For an array, use the maximum value in the array as the root node to create a maximum Binary Tree, separate the Left and Right Parts, and create the largest binary tree respectively.

Solution: Recursion

Java:

public class Solution {    public TreeNode constructMaximumBinaryTree(int[] nums) {        if (nums == null) return null;        return build(nums, 0, nums.length - 1);    }        private TreeNode build(int[] nums, int start, int end) {        if (start > end) return null;                int idxMax = start;        for (int i = start + 1; i <= end; i++) {            if (nums[i] > nums[idxMax]) {                idxMax = i;            }        }                TreeNode root = new TreeNode(nums[idxMax]);                root.left = build(nums, start, idxMax - 1);        root.right = build(nums, idxMax + 1, end);                return root;    }}

Python:

# Time:  O(n)# Space: O(n)class TreeNode(object):    def __init__(self, x):        self.val = x        self.left = None        self.right = Noneclass Solution(object):    def constructMaximumBinaryTree(self, nums):        """        :type nums: List[int]        :rtype: TreeNode        """        # https://github.com/kamyu104/LintCode/blob/master/C++/max-tree.cpp        nodeStack = []        for num in nums:            node = TreeNode(num);            while nodeStack and num > nodeStack[-1].val:                node.left = nodeStack.pop()            if nodeStack:                nodeStack[-1].right = node            nodeStack.append(node)        return nodeStack[0]

C ++:

class Solution {public:    TreeNode* constructMaximumBinaryTree(vector<int>& nums) {        if (nums.empty()) return NULL;        int mx = INT_MIN, mx_idx = 0;        for (int i = 0; i < nums.size(); ++i) {            if (mx < nums[i]) {                mx = nums[i];                mx_idx = i;            }        }        TreeNode *node = new TreeNode(mx);        vector<int> leftArr = vector<int>(nums.begin(), nums.begin() + mx_idx);        vector<int> rightArr = vector<int>(nums.begin() + mx_idx + 1, nums.end());        node->left = constructMaximumBinaryTree(leftArr);        node->right = constructMaximumBinaryTree(rightArr);        return node;    }};

C ++:

class Solution {public:    TreeNode* constructMaximumBinaryTree(vector<int>& nums) {        if (nums.empty()) return NULL;        return helper(nums, 0, nums.size() - 1);    }    TreeNode* helper(vector<int>& nums, int left, int right) {        if (left > right) return NULL;        int mid = left;        for (int i = left + 1; i <= right; ++i) {            if (nums[i] > nums[mid]) {                mid = i;            }        }        TreeNode *node = new TreeNode(nums[mid]);        node->left = helper(nums, left, mid - 1);        node->right = helper(nums, mid + 1, right);        return node;    }};

C ++:

class Solution {public:    TreeNode* constructMaximumBinaryTree(vector<int>& nums) {        vector<TreeNode*> v;        for (int num : nums) {            TreeNode *cur = new TreeNode(num);            while (!v.empty() && v.back()->val < num) {                cur->left = v.back();                v.pop_back();            }            if (!v.empty()) {                v.back()->right = cur;            }            v.push_back(cur);        }        return v.front();    }};

　　

　　

　　

 

[Leetcode] 654. Maximum Binary Tree maximum Binary Tree