PTA class a 1002

This time, you are supposed to find A+B where A and B are two polynomials.

Input Specification:

Each input file contains one test case. Each case occupies 2 lines, and each line contains the information of a polynomial:K N₁a_N1​ N₂a_N2 … N_Ka_NK where K is the number of nonzero terms in the polynomial, N_i and a_Ni(i=1,2,⋯,K) are the exponents and coefficients, respectively. It is given that 1≤K≤10,0≤N_K<⋯<N₂<N₁≤1000.

Output Specification:

For each test case you should output the sum of A and B in one line, with the same format as the input. Notice that there must be NO extra space at the end of each line. Please be accurate to 1 decimal place.

Sample Input:

2 1 2.4 0 3.2
2 2 1.5 1 0.5

Sample Output:

3 2 1.5 1 2.9 0 3.2

The first digit refers to the number of polynomials , Every two numbers form a pair , The first number in a pair is the exponent , The latter is the coefficient, that is 1.5x², That is to merge the same kind
use Map To store the corresponding index and coefficient

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.*;


public class Main {
    
    public static void main(String[] args) {
    
        Scanner sc = new Scanner(System.in);
        int numberA = sc.nextInt();
        Map<Integer, Double> map1 = new HashMap<>();
        for (int i = 0; i < numberA; i++) {
    
            Integer key = sc.nextInt();
            Double value = sc.nextDouble();
            if (map1.containsKey(key)) {
    
                map1.put(key, map1.get(key) + value);
            } else {
    
                map1.put(key, value);
            }
        }
        Map<Integer, Double> map2 = new HashMap<>();
        int numberB = sc.nextInt();
        for (int i = 0; i < numberB; i++) {
    
            Integer key = sc.nextInt();
            Double value = sc.nextDouble();
            if (map2.containsKey(key)) {
    
                map2.put(key, map2.get(key) + value);
            } else {
    
                map2.put(key, value);
            }
        }
        Map<Integer, Double> map3 = new HashMap<>(map2);
        map1.forEach((integer, aDouble) -> {
    
            if (map2.containsKey(integer)) {
    
                map3.put(integer, map1.get(integer) + map2.get(integer));
            } else {
    
                map3.put(integer, aDouble);
            }
        });
        Iterator<Map.Entry<Integer, Double>> it = map3.entrySet().iterator();
        while (it.hasNext()) {
    
            Map.Entry<Integer, Double> next = it.next();
            if (next.getValue() == 0.0) {
    
                it.remove();
            }
        }

        if ((map3.size() <= 1 && map3.containsKey(0))||map3.size() == 0) {
    
            System.out.print("0");
            return;
        } else {
    
            System.out.print(map3.size() + " ");
            List<Map.Entry<Integer, Double>> list = new ArrayList<>(map3.entrySet());
            Collections.sort(list, (o1, o2) -> o2.getKey() - o1.getKey());
            StringBuilder sb = new StringBuilder();
            for (Map.Entry<Integer, Double> maps : list) {
    
                sb.append(maps.getKey()).append(' ').append(BigDecimal.valueOf(maps.getValue()).setScale(1, RoundingMode.HALF_UP)).append(' ');
            }
            if (sb.length() > 0) {
    
                sb.deleteCharAt(sb.length() - 1);
            }
            System.out.println(sb);
        }
    }
}

There are a few disgusting points ：

1、 Keep one decimal place
2、 The last digit cannot be a space
3、 The sum of the two sets of coefficients may be zero , No more output
4、 And 3 Similar only 1 And the coefficient of this term is 0 Only output 0

（ I tried several broken formats for more than an hour There are always several test points **

To sum up
Learned a new word -> polynomials： polynomial

Traverse delete Map An element in the set needs to use Iterator To traverse the deletion instead of forEach

Iterator<Map.Entry<Integer, Double>> it = map3.entrySet().iterator();
        while (it.hasNext()) {
    
            Map.Entry<Integer, Double> next = it.next();
            if (next.getValue() == 0.0) {
    
                it.remove();
            }
        }

Customize Map The sorting of sets is based on Key still Value It can be used Collections Medium sort

List<Map.Entry<Integer, Double>> list = new ArrayList<>(map3.entrySet());
Collections.sort(list, (o1, o2) -> o2.getKey() - o1.getKey());

Yes Map Sorting of sets