蓝桥杯JAVA练习0208-BASIC16-17笔记

气死我了，写一半电脑关机了……

BASIC-16

昨天的思路大体没错，但是为了好理解我又重写了一遍
因为昨天的很繁琐所以把判断素数的函数单独拉出来了
整体思路大概就是：按要求输出等式前半部分，然后把本来就是素数的分类直接输出本身，不是素数的就从2开始除，能够整除就输出，然后取商继续除，直到商不能继续除（判断商为素数）
需要注意的是要把剩余的最后一个商输出，记得乘号

import java.util.Scanner;

public class Main {

	public static int isPrime(int n, int arr[]) {
		int i;
		int flag = 0;
		for (i = 0; i < arr.length; i++) {
			if (arr[i] == n) {
				flag = 1;
				break;
			}
		}
		if (flag == 1) {
			return 1;
		} else {
			return 0;
		}
	}

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scanner = new Scanner(System.in);
		int a = scanner.nextInt();
		int b = scanner.nextInt();
		int arr[] = new int[b];
		int i, j, k = 0;
		for (i = 2; i <= b; i++) {
			int flag = 0;
			for (j = 2; j <= Math.sqrt(i); j++) {
				if (i % j == 0) {
					flag = 1;
					break;
				}
			}
			if (flag == 0) {
				arr[k] = i;
				k++;
			}
		}
		for (i = a; i <= b; i++) {
			int cnt = 0;
			System.out.print(i + "=");
			if (Main.isPrime(i, arr) == 1) {
				System.out.print(i);
			} else {
				int num = i;
				while (Main.isPrime(num, arr) == 0) {
					for (j = 2; j <= Math.sqrt(num); j++) {
						if (num % j == 0) {
							if (cnt == 0) {
								System.out.print(j);
							} else {
								System.out.print("*" + j);
							}
							cnt++;
							break;
						}
					}
					num /= j;
				}
				System.out.print("*" + num);
			}
			System.out.println();
		}

	}

}

2021.04.12
突然看不懂自己写了啥……
就又写了一遍，这个比较好理解

import java.util.Scanner;

public class Main {

	public static int isPrime(int n) {
		int i;
		int flag = 1;
		for (i = 2; i <= Math.sqrt(n); i++) {
			if (n % i == 0) {
				flag = 0;
				break;
			}
		}
		if (flag == 1) {
			return 1;
		} else {
			return 0;
		}
	}

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scanner = new Scanner(System.in);
		int a = scanner.nextInt();
		int b = scanner.nextInt();
		int i, j;
		for (i = a; i <= b; i++) {
			if (Main.isPrime(i) == 1) {
				System.out.println(i + "=" + i);
			} else {
				System.out.print(i + "=");
				int num = i;
				int cnt = 0;
				for (j = 2; j <= Math.sqrt(i); j++) {
					if (num % j == 0) {
						if (cnt == 0) {
							System.out.print(j);
						} else {
							System.out.print("*" + j);
						}
						num = num / j;
						// System.out.println("-----" + num);
						cnt++;
						if (Main.isPrime(num) == 1) {
							System.out.print("*" + num);
							break;
						} else {
							j = 1;
						}
					}
				}
				System.out.println();
			}
		}
	}

}

BASIC-17

矩阵乘法
单独把0次和1次挑出来了（1不挑也可）
遇到两个坑（其实是粗心）

• 存储矩阵相乘结果的矩阵没有初始化
• 幂运算需要循环m次相乘，但是每次相乘都是原矩阵×原矩阵，导致样例过了但是只要次数不是2就是错的，需要再用临时矩阵存放每乘一次之后的结果，下次相乘则用临时矩阵乘原矩阵

记得幂次循环的时候要先-1（这个测试一下就找到Bug了）

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		int m = scanner.nextInt();
		long arr[][] = new long[n][n];
		long num[][] = new long[n][n];
		int i, j, k;
		for (i = 0; i < n; i++) {
			for (j = 0; j < n; j++) {
				arr[i][j] = scanner.nextInt();
				num[i][j] = arr[i][j];
			}
		}
		if (m == 0) {
			for (i = 0; i < n; i++) {
				for (j = 0; j < n; j++) {
					if (i == j) {
						System.out.print("1 ");
					} else {
						System.out.print("0 ");
					}
				}
				System.out.println();
			}
		} else if (m == 1) {
			for (i = 0; i < n; i++) {
				for (j = 0; j < n; j++) {
					System.out.print(arr[i][j] + " ");
				}
				System.out.println();
			}
		} else {
			long ans[][] = new long[n][n];
			m = m - 1;
			while (m-- != 0) {
				for (i = 0; i < n; i++) {
					for (j = 0; j < n; j++) {
						ans[i][j] = 0;
						for (k = 0; k < n; k++) {
							ans[i][j] += num[i][k] * arr[k][j];
						}
					}
				}
				for (i = 0; i < n; i++) {
					for (j = 0; j < n; j++) {
						num[i][j] = ans[i][j];
					}
				}
			}
			for (i = 0; i < n; i++) {
				for (j = 0; j < n; j++) {
					System.out.print(ans[i][j] + " ");
				}
				System.out.println();
			}
		}
	}

}