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test42.java
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46 lines (42 loc) · 1.27 KB
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package byteDance;
import java.util.ArrayList;
import java.util.List;
import java.util.Stack;
/**
* Created by lizeyang on 2020/5/16.
* 二叉排序树找第k大的元素
*/
public class test42 {
//利用二叉搜索树的特点，左<中<右，再利用中序排序即可
public static int test(TreeNode root, int k) {
if (root == null) {
return 0;
}
Stack<TreeNode> stack = new Stack<>();
List<Integer> list = new ArrayList<>();
while (!stack.isEmpty() || root != null) {
if (root != null) {
stack.push(root);
root = root.left;
} else {
root = stack.pop();
list.add(root.val);
root = root.right;
}
}
if (k > list.size() || k < 0) {
return 0;
}
return list.get(list.size() - k);
}
public static void main(String[] args) {
TreeNode root = new TreeNode(5);
root.left = new TreeNode(4);
root.right = new TreeNode(8);
root.left.left = new TreeNode(3);
root.right.left = new TreeNode(7);
root.right.left.left = new TreeNode(6);
root.right.right = new TreeNode(9);
System.out.println(test(root, 5));
}
}