Java编程基础阶段笔记day05数组
数组
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笔记Notes
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int[] age = { 1, 2, 3, 4, 5, 6 };
/*
* 数组中常见的算法
* 1. 求数组中元素的最大值、最小值、平均值、总和等
* 2. 数组的复制、反转、查找（线性查找、二分查找（了解））
* 3. 数组元素的排序算法:冒泡排序
*/
public class ArrayAlgorithm {
public static void main(String[] args) {
// 数组最大值、最小值、平均值、总和
System.out.println("---------------------------------数组最大值、最小值、平均值、总和--------------------------");
int scores[] = new int[5];
for (int i = 0; i < scores.length; i++) {
scores[i] = (int) (Math.random() * 10);
}
for (int i = 0; i < scores.length; i++) {
System.out.print(scores[i] + " ");
}
System.out.println();
int max = scores[0];
int min = scores[0];
int add = scores[0];
double ever = 0;
for (int i = 0; i < scores.length; i++) {
if (max < scores[i]) {
max = scores[i];
}
if (min > scores[i]) {
min = scores[i];
}
add += scores[i];
}
ever = add / scores.length;
System.out.println("max = " + max + " min = " + min + " add = " + add + " ever = " + ever);
System.out.println("-------------------------------------------------------------");
System.out.println("----------------------------数组复制---------------------------------------------");
int copyScores[] = new int[scores.length];
for (int i = 0; i < copyScores.length; i++) {
copyScores[i] = scores[i];
}
for (int i = 0; i < copyScores.length; i++) {
System.out.print(copyScores[i] + " ");
}
System.out.println();
System.out.println("---------------------------数组反转方法一---------------------------------------");
// 方法一
System.out.println("方法一");
int reverse[] = new int[scores.length];
for (int i = 0, j = scores.length - 1; i < scores.length && j >= 0; i++, j--) {
reverse[i] = scores[j];
}
for (int i = 0; i < reverse.length; i++) {
System.out.print(reverse[i] + " ");
}
System.out.println();
System.out.println("--------------------------");
for (int i = 0; i < scores.length; i++) {
System.out.print(scores[i] + " ");
}
System.out.println();
System.out.println("----------------------------数组反转方法二-----------------------------------");
for (int i = 0; i < scores.length / 2; i++) {
int temp = scores[i];
scores[i] = scores[scores.length - i - 1];
scores[scores.length - i - 1] = temp;
}
for (int i = 0; i < scores.length; i++) {
System.out.print(scores[i] + " ");
}
System.out.println();
System.out.println("-------------------------数组查找-线性查找-------------------------");
int[] numbers = { 1, 10, 9, 8, 20 };
// 线性查找
int findNumber = 18; // 要查找数值
int index = -1;//查找到的数值所对应的下标
for (int i = 0; i < numbers.length; i++) {
if (findNumber ==numbers[i]) {
index = i;
break;//只查找一个
}
}
if (index != -1) {
System.out.println("查找到数值！所对应的数组下标为：" + index);
} else {
System.out.println("查找不到值！");
}
System.out.println("------------------------数组查找- 二分查找--------------------------------");
int[] number2 = { 12, 30, -5, 6, 9, 10, 5 };
//排序
Arrays.sort(number2); // 必须排序好
for (int i = 0; i < number2.length; i++) {
System.out.print(number2[i] + " ");
}
System.out.println();
int findNumber2 = 12;//要查找的内容
int start = 0;
int end = number2.length-1;
int index2 = -1; //所在元素位置
while (start <= end) {
int mid = (start + end) / 2;
if (number2[mid] == findNumber2) {
index2 = mid;
break;
}
if(number2[mid] > findNumber2){
end = mid - 1;
}else {
start = mid + 1;
}
}
if (index2 != -1) {
System.out.println("你要的商品存在，在位置：" + index2);
}else {
System.out.println("客官您的包裹丟了");
}
System.out.println("------------------------------冒泡排序（必须会手写）-------------------------------------");
int[] numbers3 = {10,2,89,39,16};
for (int i = 0; i < numbers3.length; i++) {
System.out.print(numbers3[i] + " ");
}
System.out.println();
System.out.println("------------------------------排序前--------------------------------------------------------");
for (int i = 0; i < numbers3.length -1; i++) { //外排序次数为长度-1 为5-1 = 4
for (int j = 0; j < numbers3.length -1 - i; j++) { //内排序次数每次递减 4 3 2 1
if (numbers3[j] > numbers3[j+1]) {
int temp = numbers3[j];
numbers3[j] = numbers3[j+1];
numbers3[j+1] = temp;
}
}
}
System.out.println("--------------------------排序后-------------------------------------------");
for (int i = 0; i < numbers3.length; i++) {
System.out.print(numbers3[i] + " ");
}
System.out.println();
System.out.println("------------------------排序完成------------------------------------");
}
}
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总结Summary |
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