g0101_0200.s0144_binary_tree_preorder_traversal.Solution Maven / Gradle / Ivy
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Java Solution for LeetCode algorithm problems, continually updating
package g0101_0200.s0144_binary_tree_preorder_traversal;
// #Easy #Depth_First_Search #Tree #Binary_Tree #Stack #Data_Structure_I_Day_10_Tree
// #Udemy_Tree_Stack_Queue #2022_06_24_Time_1_ms_(48.38%)_Space_42_MB_(68.46%)
import com_github_leetcode.TreeNode;
import java.util.ArrayList;
import java.util.List;
import java.util.Stack;
/*
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
@SuppressWarnings("java:S1149")
public class Solution {
public List preorderTraversal(TreeNode root) {
List result = new ArrayList<>();
if (root == null) {
return result;
}
Stack stack = new Stack<>();
TreeNode current = root;
while (current != null || !stack.isEmpty()) {
while (current != null) {
result.add(current.val);
stack.push(current.right);
current = current.left;
}
current = stack.pop();
}
return result;
}
}