LeetCode 414. The third largest number (simple, array) day13

Title Description ： Give you a non empty array , Returns the value in this array The third largest number . If it doesn't exist , Then return the maximum number in the array .

Example 1：

 Input ：[3, 2, 1]
 Output ：1
 explain ： The third largest number is  1 .

Example 2：

 Input ：[1, 2]
 Output ：2
 explain ： The third largest number doesn't exist ,  So return the maximum number  2 .

Example 3：

 Input ：[2, 2, 3, 1]
 Output ：1
 explain ： Be careful , Ask to return the third largest number , It's the third largest of all the different numbers .
 There are two values in this example that are  2  Number of numbers , They're both second . The third largest of all the different numbers is  1 .

title ：

Method 1 ：TreeSet aggregate ( characteristic ： Do not repeat , No index , Sortable )

1、 Make a statement TreeSet aggregate , It is characterized by non repetition 、 No index 、 Sortable ( The default order is from small to large );
2、 Traversal array , Add array elements to the collection , because TreeSet The properties of sets , Then duplicate elements will not be added to the collection , also 
       Judge whether the element in the set is greater than 3 individual , If more than three , Use remove Method to remove the first element of the set ,
       Always keep the number of elements in the collection to 3 individual ( The premise is that the array elements should be greater than three , These three elements are the top three numbers in the set );
3、 Judge whether the number of set elements is three , If three return the first element , Otherwise, the tail element is returned .

Method 2 ：ArrayList aggregate + Sort

1、 First, sort the array ( From small to small );
2、 Add array elements to ArrayList Set and de duplication ;
3、 here ArrayList The elements in the set are arranged from small to large , Return according to the number of elements in the set .

If you are not familiar with the application of sets, you can refer to the article ：Java Medium Collection Assemble and Collection Collection implementation class instance https://blog.csdn.net/qq_43751200/article/details/123803851

Code implementation ：

import java.util.*;

public class ThirdMax {
    public static void main(String[] args) {
        int[] nums = {-2147483648,1,1};
        System.out.println(thirdMax1(nums));
    }

    //  Method 1：TreeSet aggregate 
    public static int thirdMax(int[] nums){
        // 1.  Make a statement TreeSet aggregate , Be careful TreeSet The properties of sets , No repetition , No index , Sortable ( Automatic sorting from small to large )
        TreeSet<Integer> set = new TreeSet<>();  //  Default ascending order 

        // 2.  Add elements from the array to the collection 
        for (int i = 0; i < nums.length; i++) {
            set.add(nums[i]);
           if(set.size() > 3){
               set.remove(set.first());
           }
        }

        return set.size() == 3 ? set.first() : set.last();
    }

    //  Method 1：ArrayList aggregate 
    public static int thirdMax1(int[] nums){
        Arrays.sort(nums);

        ArrayList<Integer> arrayList = new ArrayList<>();
        //  Traverse the array and remove the duplicates , Add array elements to the collection 
        for (int i = 0; i < nums.length; i++) {
            if(arrayList.contains(nums[i])){
                continue;
            }else {
                arrayList.add(nums[i]);
            }
        }

        return arrayList.size() >= 3 ? arrayList.get(arrayList.size() - 3) : arrayList.get(arrayList.size() -1);
    }
}

source ： Power button （LeetCode）
link ：https://leetcode-cn.com/problems/third-maximum-number

     source ： Power button （LeetCode）
     link ：https://leetcode-cn.com/problems/third-maximum-number
     Copyright belongs to the network . For commercial reprint, please contact the official authority , Non-commercial reprint please indicate the source . There are two values in  2  Number of numbers , They're both second . The third largest of all the different numbers is  1 .