Leetcode 系列题解（十八）

654. Maximum Binary Tree

题目内容

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].

分析

题目比较简单，按照题目的意思，进行递归构建即可，找到最大的元素作为节点的值，将左边的数组生成左子树，将右边的数组生成右子树。

代码

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