题解 | #二叉树的中序遍历#

public class Solution {
    public int[] inorderTraversal(TreeNode root) {
        Stack<TreeNode> stack = new Stack<>();
        List<Integer> list = new ArrayList<>();
        TreeNode p = root;
        while (p != null || !stack.isEmpty()) {
            if (p != null) {
                // 一直先找左孩子
                stack.push(p);
                p = p.left;
            } else {
                // 该节点没有左孩子，就去看是否有右孩子
                p = stack.pop();
                list.add(p.val);
                p = p.right;
            }
        }
        int len = list.size();
        int[] arr = new int[len];
        for (int i = 0; i < len; i ++)
            arr[i] = list.get(i);
        return arr;
    }
}

细品就OK