LintCode-----11.二叉查找树中搜索区间

import java.util.*;
import java.lang.*;

public class Solution {
/*
* @param root: param root: The root of the binary search tree
* @param k1: An integer
* @param k2: An integer
* @return: return: Return all keys that k1<=key<=k2 in ascending order
*/
public List<Integer> searchRange(TreeNode root, int k1, int k2) {
// write your code here

List<Integer> all=new ArrayList<>();

inOrder(root,all);
List<Integer> result=new ArrayList<>();
for(int i=0;i<all.size();i++){
int temp=all.get(i);
if(temp>=k1&&temp<=k2){
result.add(temp);
}
}
return result;

}

public void inOrder(TreeNode root,List<Integer> list){
if(root!=null){
inOrder(root.left,list);
list.add(root.val);
inOrder(root.right,list);
}
}
}

九章解答

private ArrayList<Integer> results;

public ArrayList<Integer> searchRange(TreeNode root, int k1, int k2) {
results = new ArrayList<Integer>();
helper(root, k1, k2);
return results;
}

private void helper(TreeNode root, int k1, int k2) {
if (root == null) {
return;
}
//当前值比k1都大，看看他的左儿子的情况，要找更小的数来比较，右边就不看了。
if (root.val > k1) {
helper(root.left, k1, k2);
}
if (root.val >= k1 && root.val <= k2) {
results.add(root.val);
}
//当前的值比k2都小，看看右儿子的情况，要找最接近k2的数，左边就不看了。
if (root.val < k2) {
helper(root.right, k1, k2);
}
}