本体意在对二叉树的构建的巩固,了解先序遍历,和二叉搜索树的概念即可解题
(速度击败100%java,内存仅击败5%)
/** * Definition for a binary tree node.
* public class TreeNode {
* * int val;
* * TreeNode left;
* * TreeNode right;
* * TreeNode(int x) { val = x; }
* * }
* */
class Solution {
private TreeNode root = new TreeNode(0);
public TreeNode bstFromPreorder(int[] preorder) {
if(preorder.length==0) return null;
root = new TreeNode(preorder[0]);
for(int i=1;i<preorder.length;i++)
fun(preorder,i);
return root;
}
public void fun(int[] preorder, int num){
int a = preorder[num];
TreeNode pos = root;
while(true){
if(pos.val>a){
if(pos.left==null) {pos.left = new TreeNodw(a);break;}
else {pos = pos.left;continue;}
}
else{
if(pos.right==null) {pos.right = new TreeNode(a);break;}
else {pos = pos.right;continue;}
}
}
}}