Binary Search Tree Iterator

最新推荐文章于 2020-12-10 02:15:35 发布

原创最新推荐文章于 2020-12-10 02:15:35 发布 · 252 阅读

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本文介绍了一种用于遍历二叉搜索树(BST)的迭代器实现方法。该迭代器通过使用栈来跟踪节点，能够有效地按升序访问BST的所有元素。文章详细解释了迭代器的初始化过程及hasNext和next方法的具体实现。

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/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

public class BSTIterator {

    Stack<TreeNode> stack;
    public BSTIterator(TreeNode root) {
        stack = new Stack<>();
        while (root != null) {
            stack.push(root);
            root = root.left;
        }
    }

    /** @return whether we have a next smallest number */
    public boolean hasNext() {
        return !stack.isEmpty();
    }

    /** @return the next smallest number */
    public int next() {
        TreeNode smallest = stack.pop();
        if (smallest.right != null) {
            TreeNode right = smallest.right;
            while (right != null) {
                stack.push(right);
                right = right.left;
            }
        }
        return smallest.val;
    }
}

/**
 * Your BSTIterator will be called like this:
 * BSTIterator i = new BSTIterator(root);
 * while (i.hasNext()) v[f()] = i.next();
 */