# 108.convert-sorted-array-to-binary-search-tree

## Statement

``````输入：nums = [-10,-3,0,5,9]

``````

``````输入：nums = [1,3]

``````

• `1 <= nums.length <= 104`
• `-104 <= nums[i] <= 104`
• `nums`严格递增 顺序排列

Given an integer array `nums` where the elements are sorted in ascending order, convert it to a height-balanced binary search tree.

A height-balanced binary tree is a binary tree in which the depth of the two subtrees of every node never differs by more than one.

Example 1:

``````Input: nums = [-10,-3,0,5,9]
Output: [0,-3,9,-10,null,5]
Explanation: [0,-10,5,null,-3,null,9] is also accepted:

``````

Example 2:

``````Input: nums = [1,3]
Output: [3,1]
Explanation: [1,null,3] and [3,1] are both height-balanced BSTs.
``````

Constraints:

• `1 <= nums.length <= 104`
• `-104 <= nums[i] <= 104`
• `nums` is sorted in a strictly increasing order.

## Solution

``````#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#define endl "\n"
#define fi first
#define se second
#define all(x) begin(x), end(x)
#define rall rbegin(a), rend(a)
#define bitcnt(x) (__builtin_popcountll(x))
#define complete_unique(a) a.erase(unique(begin(a), end(a)), end(a))
#define mst(x, a) memset(x, a, sizeof(x))
#define MP make_pair

using ll = long long;
using ull = unsigned long long;
using db = double;
using ld = long double;
using VLL = std::vector<ll>;
using VI = std::vector<int>;
using PII = std::pair<int, int>;
using PLL = std::pair<ll, ll>;

using namespace __gnu_pbds;
using namespace std;
template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
const ll mod = 1e9 + 7;

template <typename T, typename S>
inline bool chmax(T &a, const S &b) {
return a < b ? a = b, 1 : 0;
}

template <typename T, typename S>
inline bool chmin(T &a, const S &b) {
return a > b ? a = b, 1 : 0;
}

#ifdef LOCAL
#include <debug.hpp>
#else
#define dbg(...)
#endif

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode() : val(0), left(nullptr), right(nullptr) {}
*     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
*     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/

#ifdef LOCAL
struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode() : val(0), left(nullptr), right(nullptr) {}
TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
};
#endif

class Solution {
public:
TreeNode *sortedArrayToBST(vector<int> &nums) {
int n = nums.size();
auto rt = new TreeNode();

auto dfs = [&](auto self, int l, int r, TreeNode *rt) -> void {
int mid = (l + r) >> 1;
rt->val = nums[mid];
if (l < mid) {
rt->left = new TreeNode();
self(self, l, mid - 1, rt->left);
}

if (mid < r) {
rt->right = new TreeNode();
self(self, mid + 1, r, rt->right);
}
};

dfs(dfs, 0, n - 1, rt);
return rt;
}
};

#ifdef LOCAL

int main() {
return 0;
}

#endif
``````