DAY 5

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数组

1.数组的声明和创建

2.内存和分析

数组定义、for each循环、求和、打印、转置、

package abb;

import java.util.Arrays;

public class a {
public static void main(String[] args) {
int[] a = new int[3];
a[2] = 1;
System.out.println(a[2]);
//写法一
int[] bb = new int[10];
//写法二
int[] cc;
cc = new int[20];
//赋值
bb[0] = 2;
bb[1] = 2;
bb[2] = 2;
bb[3] = 2;
bb[4] = 2;
bb[5] = 2;
bb[6] = 2;
bb[7] = 2;
bb[9] = 12;
//写法三****
int[] d = {1, 2, 3, 4, 5};//数组长度a[0]=第一个，因此a[4]=5为最终位
System.out.println(d[0]);
int g = 0;
for (int e = 0; e < d.length; e++) {//for each循环；打印全部数组
System.out.print("数组第" + e + "为=" + d[e]);
}
System.out.println("\n");
for (int f = 0; f < d.length; f++) {//for each循环;计算所有元素和
g = g + d[f];
}
int k = d[0];
for (int h = 0; h < d.length; h++) {//for each循环；查找最大元素
if (d[h] > k) {
k = d[h];
}
}
System.out.println("max=" + k);
System.out.println("sum=" + g);
System.out.println(bb[8]);
//计算数组数字和
int c = 0;
for (int b = 0; b < bb.length; b++) {
c = bb[b];
}
System.out.println(c);
System.out.println();
reverse(d);
int[] reverse=reverse(d);
System.out.println(Arrays.toString(reverse));
printarrays(d);
}
//反转数组
public static int[]reverse(int[] g) {//定义方法
int[] result=new int [g.length];//定义数组
for(int i =0,j=result.length-1;i<g.length;i++,j--){//反转循环
result[j]=g[i];
}
return result;
}
public static int printarrays(int[] m) {
for (int o = 0; o < m.length; o++) {
System.out.println(m[o]);
}
return 0;}

    }

package abb;

import java.util.Arrays;

import static java.util.Arrays.fill;

public class a13duoweishuzu {
public static void main(String[] args) {
/*
1,2
3,4
5,6
7,8
*/
int[][] a={{1,2},{3,4},{5,6},{7,8}};
int[] b={1,2,3,4,5};
System.out.println(a[0].length);
System.out.println(a.length);
printArrays(a);
System.out.print(Arrays.toString(b));;
//数组赋值
Arrays.fill(b,0);
System.out.print("\n");
System.out.print(Arrays.toString(b));
}
//打印二维数组
public static void printArrays (int[][] b) {
for(int i=0;i<b.length;i++){
for (int j=0;j<b[i].length;j++){
System.out.print(b[i][j]+",");
}
}
}

}

package basic;

public class a18xishushuzu {
public static void main(String[] args) {
//1.创建一个二维数组，11*11
int[][] array1 = new int[11][11];
array1[1][2] = 1;
array1[2][3] = 2;
//输出原有的数组
System.out.println("输出原有数组：");
for (int[] ints : array1) {
for (int anInt : ints) {
System.out.print(anInt + "\t");
}
System.out.println();
}
//转换为稀疏数组保存
//获取有效数字的值
int sum = 0;
for (int i = 0; i < 11; i++) {
for (int j = 0; j < 11; j++) {
if (array1[i][j] != 0) {
sum++;
}
}

    }
    System.out.println("有效值个数：" + sum);
    //2.创建一个稀疏数组的数类
    int[][] array2 = new int[sum + 1][3];
    array2[0][0] = 11;
    array2[0][1] = 11;
    array2[0][2] = sum;
    //遍历二维数组，将非0的值，存放在稀疏数组中
    int count = 0;
    for (int i = 0; i < array1.length; i++) {
        for (int j = 0; j < array1[i].length; j++) {
            if (array1[i][j]!=0){
                count++;
                array2[count][0]=i;
                array2[count][1]=j;
                array2[count][2]=array1[i][j];
            }
        }
    }
    //输出稀疏数组
    System.out.println("稀疏数组");
    for(int i=0;i<array2.length;i++){
        System.out.println(array2[i][0]+"\t"
        +array2[i][1]+"\t"
        +array2[i][2]+"\t");
        }
    System.out.println("==========");
    System.out.println("还原的操作");
    //1.读取数组
    int [][] array3=new int[array2[0][0]][array2[0][1]];
    //2.给其中的元素还原他的值
    for(int i= 1;i<array2.length;i++){
        array3[array2[i][0]][array2[i][1]]=array2[i][2];
    }//打印还原的数组
    System.out.println("打印还原的数组");
    for(int[] ints :array3){
        for(int anInt:ints){
            System.out.print(anInt+"\t");
        }
        System.out.println();
    }
    }
}