leetcode 653 两数之和IV 输入BST
作者:互联网
package com.example.lettcode.test;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
/**
* @Class FindTarget
* @Description 653 两数之和IV 输入BST
* 给定一个二叉搜索树和一个目标结果,
* 如果 BST 中存在两个元素且它们的和等于给定的目标结果,则返回 true。
* <p>
* 案例 1:
* 输入:
* 5
* / \
* 3 6
* / \ \
* 2 4 7
* Target = 9
* 输出: True
* <p>
* 案例 2:
* 输入:
* 5
* / \
* 3 6
* / \ \
* 2 4 7
* Target = 28
* 输出: False
* @Author
* @Date 2020/7/20
**/
public class FindTarget {
static class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) {
val = x;
}
}
}
/**
* 解法1: 先中序得到一个非递减的序列,然后再判断
*/
public static boolean findTarget(TreeNode root, int k) {
boolean flag = false;
List<Integer> integerList = new ArrayList<>();
inOrder(root, integerList);
int p = 0, q = integerList.size() - 1;
while (p < q) {
int tmp = integerList.get(p) + integerList.get(q);
if (tmp == k) return true;
if (tmp > k) q--;
else if (tmp < k) p++;
}
return false;
}
public static void inOrder(TreeNode root, List<Integer> integerList) {
if (root == null) return;
inOrder(root.left, integerList);
integerList.add(root.val);
inOrder(root.right, integerList);
}
/**
* 解法2:利用HashSet 保存已经遍历到的元素,判断是否存在与当前元素之和为目标值的元素
* 存在即返回false,否则加入到set中并遍历左右子树
* 使用类静态变量时每一个测试用例执行结束需要清除,否则会重复保存之前的记录
* 或者使用类成员变量
*/
static Set<Integer> integerSet = new HashSet<>();
public static boolean findTarget(TreeNode root, int k) {
if (root == null) return false;
int tmp = k - root.val;
if (integerSet.contains(tmp)) return true;
integerSet.add(root.val);
return findTarget(root.left, k) || findTarget(root.right, k);
}
// 测试用例
public static void main(String[] args) {
TreeNode root = new TreeNode(5);
TreeNode treeNode02 = new TreeNode(3);
TreeNode treeNode03 = new TreeNode(6);
root.left = treeNode02;
root.right = treeNode03;
TreeNode treeNode04 = new TreeNode(2);
TreeNode treeNode05 = new TreeNode(4);
treeNode02.left = treeNode04;
treeNode02.right = treeNode05;
TreeNode treeNode06 = new TreeNode(7);
treeNode05.right = treeNode06;
int target = 9;
boolean ans = findTarget(root, target);
integerSet.clear();
System.out.println("FindTarget demo01 result:" + ans);
target = 28;
ans = findTarget(root, target);
integerSet.clear();
System.out.println("FindTarget demo02 result:" + ans);
root = new TreeNode(1);
target = 2;
ans = findTarget(root, target);
integerSet.clear();
System.out.println("FindTarget demo03 result:" + ans);
}
标签:TreeNode,BST,integerList,IV,findTarget,int,new,root,两数 来源: https://www.cnblogs.com/fyusac/p/13343903.html