冒泡排序
/**
* 冒泡排序
* 保证最大值在最后面
*
* @param arrs
*/
static void bubbleSort(int[] arrs) {
beforeSort(arrs);
for (int i = 0; i < arrs.length; i++) {
for (int j = 0; j < arrs.length - 1 - i; j++) {
if (arrs[j] > arrs[j + 1]) {
int temp = arrs[j];
arrs[j] = arrs[j + 1];
arrs[j + 1] = temp;
}
printHint(arrs, i, j);
}
System.out.println();
}
}
选择排序
/**
* 选择排序
* 保证最左边的最小
*
* @param arrs
*/
private static void selectSort(int[] arrs) {
beforeSort(arrs);
for (int i = 0; i < arrs.length - 1; i++) {
for (int j = i + 1; j < arrs.length; j++) {
if (arrs[i] > arrs[j]) {
int temp = arrs[j];
arrs[j] = arrs[i];
arrs[i] = temp;
}
printHint(arrs, i, j);
}
System.out.println();
}
}
优化选择排序
/**
* 大大的减少数组变动次数
*
* @param arrs
*/
private static void betterSelectSort(int[] arrs) {
beforeSort(arrs);
for (int i = 0; i < arrs.length - 1; i++) {
int k = i;
for (int j = i + 1; j < arrs.length; j++) {
if (arrs[k] > arrs[j]) k = j;
}
if (k != i) {
int temp = arrs[i];
arrs[i] = arrs[k];
arrs[k] = temp;
}
System.out.print("第" + (i + 1) + "次遍排序:" + "\t\t");
for (int x : arrs) {
System.out.print(x + "\t");
}
System.out.println();
}
}
插入排序
/**
* 插入排序,认为左边的数是有序数列
*
* @param arrs
*/
private static void insertSort(int[] arrs) {
beforeSort(arrs);
int count = 0;
for (int i = 1; i < arrs.length; i++) {
for (int j = i; j > 0; j--) {
if (arrs[j] < arrs[j - 1]) {
int temp = arrs[j - 1];
arrs[j - 1] = arrs[j];
arrs[j] = temp;
} else {
break;
}
System.out.print("第" + ++count + "次遍排序:" + "\t\t");
for (int x : arrs) {
System.out.print(x + "\t");
}
}
System.out.println();
}
}
排序案例
public class Demo{
private static final int[] arrs = {45, 12, 46, 20, 48, 33};
public static void main(String[] args) {
//冒泡排序
//bubbleSort(arrs);
//选择排序
//selectSort(arrs);
//简化版选择排序
//betterSelectSort(arrs);
//插入排序
insertSort(arrs);
}
/**
* 冒泡排序
* 保证最大值在最后面
*
* @param arrs
*/
static void bubbleSort(int[] arrs) {
beforeSort(arrs);
for (int i = 0; i < arrs.length; i++) {
for (int j = 0; j < arrs.length - 1 - i; j++) {
if (arrs[j] > arrs[j + 1]) {
int temp = arrs[j];
arrs[j] = arrs[j + 1];
arrs[j + 1] = temp;
}
printHint(arrs, i, j);
}
System.out.println();
}
}
/**
* 选择排序
* 保证最左边的最小
*
* @param arrs
*/
private static void selectSort(int[] arrs) {
beforeSort(arrs);
for (int i = 0; i < arrs.length - 1; i++) {
for (int j = i + 1; j < arrs.length; j++) {
if (arrs[i] > arrs[j]) {
int temp = arrs[j];
arrs[j] = arrs[i];
arrs[i] = temp;
}
printHint(arrs, i, j);
}
System.out.println();
}
}
/**
* 大大的减少数组变动次数
*
* @param arrs
*/
private static void betterSelectSort(int[] arrs) {
beforeSort(arrs);
for (int i = 0; i < arrs.length - 1; i++) {
int k = i;
for (int j = i + 1; j < arrs.length; j++) {
if (arrs[k] > arrs[j]) k = j;
}
if (k != i) {
int temp = arrs[i];
arrs[i] = arrs[k];
arrs[k] = temp;
}
System.out.print("第" + (i + 1) + "次遍排序:" + "\t\t");
for (int x : arrs) {
System.out.print(x + "\t");
}
System.out.println();
}
}
/**
* 插入排序,认为左边的数是有序数列
*
* @param arrs
*/
private static void insertSort(int[] arrs) {
beforeSort(arrs);
int count = 0;
for (int i = 1; i < arrs.length; i++) {
for (int j = i; j > 0; j--) {
if (arrs[j] < arrs[j - 1]) {
int temp = arrs[j - 1];
arrs[j - 1] = arrs[j];
arrs[j] = temp;
} else {
break;
}
System.out.print("第" + ++count + "次遍排序:" + "\t\t");
for (int x : arrs) {
System.out.print(x + "\t");
}
}
System.out.println();
}
}
/**
* 这体现代码，复用
*
* @param arrs
*/
private static void beforeSort(int[] arrs) {
System.out.print("排序前:\t\t\t");
for (int k : arrs) {
System.out.print(k + "\t");
}
System.out.println();
}
/**
* 这体现代码，复用
* 同样你也可以把数组交换的代码抽做一个方法，
*
* @param arrs
* @param i
* @param j
*/
private static void printHint(int[] arrs, int i, int j) {
System.out.print("第" + (i + 1) + "次" + "第" + (j + 1) + "遍排序:" + "\t\t");
for (int k : arrs) {
System.out.print(k + "\t");
}
}
}
二分法查找
二分法查找的前提是数组必须是有序的；
二分查找案例
public class Demo {
private static final int[] arrs = {45, 12, 46, 20, 48, 33};
private static final int[] arrs1 = {45, 12, 46, 20, 48, 33};
public static void main(String[] args) {
//首先排序数组
insertSort(arrs);
sop(arrs);
//查找
int index = binaryFind(arrs, 20);
int index2 = binaryFind(arrs, 90);
sop(index, 20);
sop(index2, 90);
System.out.println("================系统自带的Arrays类=================");
Arrays.sort(arrs1);
System.out.println(Arrays.toString(arrs1));
System.out.println("20查找的位置：" + Arrays.binarySearch(arrs1, 20));
System.out.println("90查找的位置：" + Arrays.binarySearch(arrs1, 90));
}
private static void sop(int index, int key) {
System.out.println();
if (index != -1) {
System.out.println(key + "的位置为:" + index);
} else {
System.out.println("没有找到" + key + "的位置");
}
}
private static int binaryFind(int[] arrs, int key) {
//数组操作 下标是关键
//定义下标
int min = 0;//最小值下标
int max = arrs.length - 1;//最大值下标
int mid = arrs.length / 2;//中间值下标
while (min < max) {//查找的终止条件
if (arrs[mid] > key) {//表明key在数组前部分
max = mid - 1;
} else if (arrs[mid] < key) {//表明key在数组后半部分
min = mid + 1;
} else {
return mid;//找到下标
}
mid = (min + max) / 2;//中间下标也要改变
}
return -1;
}
private static void sop(int[] arrs) {
System.out.println("排序后:");
for (int k : arrs) {
System.out.print(k + "\t");
}
}
private static void insertSort(int[] arrs) {
for (int i = 1; i < arrs.length; i++) {
for (int j = i; j > 0; j--) {
if (arrs[j] < arrs[j - 1]) {
int temp = arrs[j - 1];
arrs[j - 1] = arrs[j];
arrs[j] = temp;
} else {
break;
}
}
}
}
}