二叉树算法之【中序遍历】

目录

LeetCode-94题

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LeetCode-94题

给定一个二叉树的根节点root，返回它的中序遍历结果。

class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> result = new ArrayList<>();
        order(root, result);
        return result;
    }

    private void order(TreeNode root, List<Integer> mid) {
        //当前节点
        TreeNode curr = root;
        //借助栈
        LinkedList<TreeNode> stack = new LinkedList<>();
        //最近一次pop的元素
        TreeNode pop = null;
        while (curr != null || !stack.isEmpty()) {
            if (curr != null) {
                stack.push(curr);
                //待处理左节点
                curr = curr.left;
            } else {
                //栈不为空
                TreeNode peek = stack.peek();
                //右节点为空
                if (peek.right == null) {
                    mid.add(peek.val);
                    pop = stack.pop();
                }
                //右节点处理完
                else if (peek.right == pop) {
                    pop = stack.pop();
                }
                //处理右节点
                else {
                    mid.add(peek.val);
                    curr = peek.right;
                }
            }
        }
    }
}