代码随想录算法刷题训练营day21：LeetCode(501)二叉搜索树中的众数、LeetCode(530)二叉搜索树的最小绝对差

LeetCode(501)二叉搜索树中的众数
题目

代码

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int[] findMode(TreeNode root) {
        //定义一个集合存储数据
        List<Integer> dateTree=new ArrayList<>();
        getDateTree(root,dateTree);
        Map<Integer,Integer> mapTreedate=new HashMap<>();
        for(int i=0;i<dateTree.size();i++){
            int tempDate=dateTree.get(i);
            if(mapTreedate.containsKey(tempDate)){
                mapTreedate.put(tempDate,mapTreedate.get(tempDate)+1);
            }else{
                mapTreedate.put(tempDate,1);
            }
        }
        //用Map集合存储数据
        int count=0;
        for(Map.Entry<Integer,Integer> entry:mapTreedate.entrySet()){
            int key=entry.getKey();
            int countValue=entry.getValue();
            if(countValue>=count){
                count=countValue;
            }
        }
        List<Integer> resultDate=new ArrayList<>();
        for(Map.Entry<Integer,Integer> entry:mapTreedate.entrySet()){
            if(entry.getValue().equals(count)){
                resultDate.add(entry.getKey());
            }
        }
        int[] result=new int[resultDate.size()];
        for(int i=0;i<resultDate.size();i++){
            result[i]=resultDate.get(i);
        }
        return result;
    }
    //遍历树
    public void getDateTree(TreeNode root,List<Integer> dateTree){
        if(root==null){
            return;
        }
        dateTree.add(root.val);
        getDateTree(root.left, dateTree);
        getDateTree(root.right, dateTree);
    }

}

LeetCode(530)二叉搜索树的最小绝对差
题目

代码

import java.util.ArrayList;
import java.util.List;

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int getMinimumDifference(TreeNode root) {
        List<Integer> dateTree=new ArrayList<>();
        getTreeDate(root,dateTree);
        int minDate=Math.abs(dateTree.get(0)-dateTree.get(1));
        for (int i = 0; i < dateTree.size(); i++) {
            for(int j=i+1;j<dateTree.size();j++){
                int tempDate=Math.abs(dateTree.get(i)-dateTree.get(j));
                if(tempDate<minDate){
                    minDate=tempDate;
                }
            }        
        }
        return minDate;
    }
    public void getTreeDate(TreeNode root,List<Integer> dateTree){
        if(root==null){
            return;
        }
        dateTree.add(root.val);//中序
        getTreeDate(root.left, dateTree);
        getTreeDate(root.right, dateTree);
    }
}