👩‍🏫 地址

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1. 蘑菇炸弹

👩‍🏫 蘑菇炸弹

🎉 AC code

import java.util.Scanner;

public class Main
{
	public static void main(String[] args)
	{
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n];
		for (int i = 0; i < n; i++)
			a[i] = sc.nextInt();
		int cnt = 0;
		for (int i = 1; i < n - 1; i++)
			if (a[i] >= a[i - 1] + a[i + 1])
				cnt++;
		System.out.println(cnt);
	}
}

2. 构造数字

👩‍🏫 构造数字

🎉 AC code

import java.util.Scanner;

public class Main
{
	public static void main(String[] args)
	{
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		char[] ans = new char[n];
		for (int i = 0; i < n; i++)
		{
			if (m > 0)
			{
				if (m >= 9)
				{
					ans[i] = (char) (9 + '0');
					m -= 9;
				} else
				{
					ans[i] = (char) (m + '0');
					m = 0;
				}
			} else
			{
				ans[i] = '0';
			}
		}
//		System.out.println(ans[0]);
		System.out.println(String.valueOf(ans));
	}
}

3. 小蓝的金牌梦

👩‍🏫 题目地址

🎉 AC code

import java.util.HashSet;
import java.util.Scanner;

public class Main
{
	static int N = 100010;
	static boolean[] st = new boolean[N];
	static int[] p = new int[N];
	static int cnt = 0;

	static void init(int n)
	{
		for (int i = 2; i <= n; i++)
		{
			if (!st[i])
				p[cnt++] = i;
			
			for (int j = 0; p[j] <= n / i; j++)
			{
				st[p[j] * i] = true;
				if (i % p[j] == 0)
					break;
			}
		}
	}

	public static void main(String[] args)
	{
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		init(n);
		int[] a = new int[n + 1];
		long[] s = new long[n + 1];
		s[0] = 0;
		for (int i = 1; i <= n; i++)
		{
			a[i] = sc.nextInt();
			s[i] = s[i - 1] + a[i];
		}
		long ans = Long.MIN_VALUE;
		for (int i = 0; i < cnt; i++)
		{
			int len = p[i];
			for (int j = 0; j + len <= n; j++)
			{
				long x = s[j + len] - s[j];
				ans = ans < x ? x : ans;
			}
		}
		System.out.println(ans);

	}
}

4. 合并石子

⭐ 思路

找规律：最基础的三个a.b,c，不管是 a * b + (a+b)* c还是另一种选择a * c + (a+c) * b，不难发现两者完全相等（前缀和）

🎉 AC code

import java.util.*;
import java.math.BigInteger;
// 1:无需package
// 2: 类名必须Main, 不可修改

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n];
        for (int i = 0; i < n; i++) a[i] = sc.nextInt();
        BigInteger ans = new BigInteger("0");
        BigInteger sum = new BigInteger(String.valueOf(a[0]));
        for (int i = 0; i < n - 1; i++) {
          ans = ans.add(sum.multiply(new BigInteger(String.valueOf(a[i+1]))));
          sum = sum.add(new BigInteger(String.valueOf(a[i + 1])));
        }
        System.out.println(ans);
        sc.close();
  }
}