[Programmers]最大数-JAVA

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📚 Problem


大数
  • 0または正の整数が与えられた場合、接続可能な整数の最大数を探す
  • numbers長さが1以上100000以下
  • numbersの元素が0以上1000以下

    • 📝 Solution


    Key Idea
  • ・숫자로 0만 주어지는 배열配列の和を求め、0は「0」
  • 要素の中で最も長い数字の長さは4そのため、元の数字を繰り返して生成した上位4桁を対象に記憶する
  • 上で得られた数字を比較して、大きいのを前に並べる.
  • 上記の数字が同じなら、元の数字が少ない順に並べば最大の数字が得られる
    •     public String solution(int[] numbers) {
        ArrayList<Number> list = new ArrayList<>();
        StringBuilder builder = new StringBuilder();

        if(Arrays.stream(numbers).sum() == 0)
            return "0";

        for (int number : numbers)
            list.add(new Number(Integer.toString(number)));

        for (Number number : list)
            number.setChanged();

        list.sort((o1, o2) -> {
            if (o1.changed.equals(o2.changed))
                return Integer.parseInt(o1.original) - Integer.parseInt(o2.original);
            return Integer.parseInt(o2.changed) - Integer.parseInt(o1.changed);
        });

        for(Number number : list)
            builder.append(number.original);

        return builder.toString();
    }

    💻 Code


    Solution.java

    import java.util.ArrayList;
import java.util.Arrays;

class Number {
    String original;
    String changed;

    public Number(String original) {
        this.original = original;
    }

    public void setChanged() {
        StringBuilder builder = new StringBuilder();

        while (builder.toString().length() <= 4)
            builder.append(original);

        changed = builder.substring(0, 4);
    }
}

class Solution {
    public String solution(int[] numbers) {
        ArrayList<Number> list = new ArrayList<>();
        StringBuilder builder = new StringBuilder();

        if(Arrays.stream(numbers).sum() == 0)
            return "0";

        for (int number : numbers)
            list.add(new Number(Integer.toString(number)));

        for (Number number : list)
            number.setChanged();

        list.sort((o1, o2) -> {
            if (o1.changed.equals(o2.changed))
                return Integer.parseInt(o1.original) - Integer.parseInt(o2.original);
            return Integer.parseInt(o2.changed) - Integer.parseInt(o1.changed);
        });

        for(Number number : list)
            builder.append(number.original);

        return builder.toString();
    }
}

    SolutionTest.java

    import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

import static org.junit.jupiter.api.Assertions.assertEquals;

public class SolutionTest {
    Solution solution;

    @BeforeEach
    public void setSol(){
        solution = new Solution();
    }

    @Test
    public void solution_1(){
        String result = solution.solution(new int[]{6,10,2});
        assertEquals("6210", result);
    }

    @Test
    public void solution_2(){
        String result = solution.solution(new int[]{3,30,34,5,9});
        assertEquals("9534330", result);
    }

    @Test
    public void solution_3(){
        String result = solution.solution(new int[]{1, 10, 100, 1000});
        assertEquals("1101001000", result);
    }

    @Test
    public void solution_4(){
        String result = solution.solution(new int[]{9,998});
        assertEquals("9998", result);
    }

    @Test
    public void solution_5(){
        String result = solution.solution(new int[]{30,3021});
        assertEquals("303021", result);
    }
}
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