20150707 lintcode 总结 Search Range in Binary Search Tree

最新推荐文章于 2018-08-08 14:59:50 发布

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本文介绍了一种在二叉搜索树中查找指定区间内所有元素的方法。通过递归遍历树结构，当树节点值位于指定范围内时，将该值加入结果列表，并继续遍历左右子树，确保所有符合条件的节点都被找到。

Given two values k1 and k2 (where k1 < k2) and a root pointer to a Binary Search Tree. Find all the keys of tree in range k1 to k2. i.e. print all x such that k1<=x<=k2 and x is a key of given BST. Return all the keys in ascending order.

Example

If k1 = 10 and k2 = 22, then your function should return [12, 20, 22].

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of the binary search tree.
     * @param k1 and k2: range k1 to k2.
     * @return: Return all keys that k1<=key<=k2 in ascending order.
     */
    private ArrayList<Integer> results = new ArrayList<Integer> ();
    public ArrayList<Integer> searchRange(TreeNode root, int k1, int k2) {
        // write your code here
        helper(root, k1, k2);
        return results;
    }
    
    private void helper(TreeNode root, int k1, int k2) {
        if (root == null) {
            return;
        }
        if (root.val > k1) {
            helper(root.left, k1, k2);
        }
        if (root.val >= k1 && root.val <= k2) {
            results.add(root.val);
        }
        if (root.val < k2) {
            helper(root.right, k1, k2);
        }

    }
}

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