从零开始学Java（打卡第18天）

目标开发一款自己喜欢且能最大限度让用户参与建设的社交软件。

 笔记：

二维数组的遍历：

public class TwoDimensionalArray {
	public static void main(String[] args) {
		int[][] arr = {{4, 6},{1, 4, 5, 7},{-2}};
		int sum = 0;
		for (int i = 0; i < arr.length; i++) {
			for (int j = 0; j < arr[i].length; j++) {
				sum += arr[i][j];
			}
		}
		System.out.println("sum=" + sum);
	}
}

练习：使用二维数组打印一个10行的杨辉三角：

public class TwoDimensionalArray {
	public static void main(String[] args) {
		int[][] arr = new int[10][];
		for (int i = 0; i < arr.length; i++) {
			arr[i] = new int[i + 1];
			for (int j = 0; j < arr[i].length; j++) {
				if (j == 0 || j == arr[i].length - 1) {
					arr[i][j] = 1;
				} else {
					arr[i][j] = arr[i - 1][j] + arr[i - 1][j - 1];
				}
			}
		}
		for (int i = 0; i < arr.length; i++) {
			for (int j = 0; j < arr[i].length; j++) {
				System.out.print(arr[i][j] + " ");
			}
			System.out.println();	
		}
	}
}

 本章作业：

 3、在一个有序数列中插入一个任意数，插入后仍保持有序排列（两种方法）

import java.util.Scanner;
public class TwoDimensionalArray {
	public static void main(String[] args) {
		Scanner myScanner = new Scanner(System.in);
		int[] arr1 = {10, 12, 45, 90};
		int[] arr2 = new int[arr1.length + 1];
		for (int i = 0; i < arr1.length; i++) {
			arr2[i] = arr1[i];
		}
		System.out.println("请输入您要添加的数字");
		int num = myScanner.nextInt();
		arr2[arr2.length - 1] = num;
		arr1 = arr2;
		int temp = 0;
		for (int i = 0; i < arr1.length - 1; i++) {
			for (int j = 0; j < arr1.length - 1 - i; j++) {
				if (arr1[j] > arr1[j + 1]) {
					temp = arr1[j];
					arr1[j] = arr1[j + 1];
					arr1[j + 1] = temp;
				} 
			}
		}
		for (int i = 0; i < arr1.length; i++) {
			System.out.print(arr1[i] + " ");
		}
	}
}