leetcode:(94) Binary Tree Inorder Traversal(java)

package HashTable;

/**
 * 题目：
 *      Given a binary tree, return the inorder traversal of its nodes' values.
 * 解题思路：
 *      从根节点开始，先将根节点压入栈，然后再将其所有左子结点压入栈，然后取出栈顶节点，保存节点值，
 *      再将当前指针移到其右子节点上，若存在右子节点，则在下次循环时又可将其所有左子结点压入栈中。
 *      这样就保证了访问顺序为左-根-右
 */

import java.util.ArrayList;
import java.util.List;
import java.util.Stack;

public class InorderTraversal_94_1019 {
    public List<Integer> InorderTraversal(TreeNode root) {
        List<Integer> result = new ArrayList<>();
        Stack<TreeNode> stack = new Stack<>();

        TreeNode cur = root;
        while (cur != null || !stack.empty()) {
            while (cur != null) {
                stack.push(cur);
                cur = cur.left;
            }

            cur = stack.pop();
            result.add(cur.val);
            cur = cur.right;
        }

        return result;
    }

    public static void main(String[] args) {
        TreeNode root = new TreeNode(1);
        TreeNode node1 = new TreeNode(2);
        TreeNode node2 = new TreeNode(3);

        root.right = node1;
        node1.left = node2;

        InorderTraversal_94_1019 test = new InorderTraversal_94_1019();
        List<Integer> result = test.InorderTraversal(root);
        System.out.println(result);
    }
}