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BST_ArrayToBST.java
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BST_ArrayToBST.java
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import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
// https://practice.geeksforgeeks.org/problems/array-to-bst/0
// https://www.geeksforgeeks.org/sorted-array-to-balanced-bst/
// https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/
// https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/discuss/35220/My-Accepted-Java-Solution
class BST_ArrayToBST {
private static TreeNode buildBSTFromSortedArray(int[] ip) {
if(ip.length == 0) return null;
int left = 0;
int right = ip.length-1;
return buildBST(ip, left, right);
}
private static TreeNode buildBST(int[] ip, int left, int right) {
if(left > right) return null;
int mid = left + (right - left) / 2;
TreeNode root = new TreeNode(ip[mid]);
root.left = buildBST(ip, left, mid-1);
root.right = buildBST(ip, mid+1, right);
return root;
}
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int t = Integer.parseInt(br.readLine().trim());
while(t-->0) {
int n = Integer.parseInt(br.readLine().trim());
String[] str = br.readLine().trim().split("\\s+");
int[] ip = new int[n];
for(int i = 0; i < n; i++) {
ip[i] = Integer.parseInt(str[i]);
}
TreeNode root = buildBSTFromSortedArray(ip);
StringBuilder sb = new StringBuilder();
printTree(root, sb);
System.out.println(sb);
}
}
static void printTree(TreeNode root, StringBuilder sb) {
if(root == null) return;
sb.append(root.data).append(" ");
printTree(root.left, sb);
printTree(root.right, sb);
}
static class TreeNode {
int data;
TreeNode left;
TreeNode right;
TreeNode(int data) {
this.data = data;
left = right = null;
}
}
}