public class Jiecheng {
public static void main(String[] args) {
System.out.println(jiecheng(5));
}
public static int jiecheng(int n){
if(n == 1){
return 1;
}else{
return n * jiecheng(n - 1);
}
}
}
可以利用方法返回调用方法本身解决一些难题
重点注意递归的结束条件即可
import java.util.Scanner;
import java.util.ArrayList;
public class BinarySearchPractice {
public static void main(String[] args) {
ArrayList<Integer> list = new ArrayList<>();
Scanner sc = new Scanner(System.in);
while (true) {
System.out.println("你所想要添加的数字为(键入-1即停止)：");
int num = sc.nextInt();
if (num == -1) {
break;
}
list.add(num);
}
int[] arr = new int[list.size()];
for (int i = 0; i < list.size(); i++) {
arr = list.get(i);
}
System.out.println("请输入你想检索的数字：");
int num1 = sc.nextInt();
sort(arr);
System.out.println("已将你所输入数字冒泡排序（升序），结果为：");
printArray(arr);
System.out.println("开始二分查询");
System.out.print(binarySearch(arr, 0, arr.length - 1, num1) + 1);
System.out.println("位为本数字位列数字位置");
System.out.println("若结果为0则表明本数组内不含该数字");
}
二分法只能查询升序数组元素，所以先对目标数组进行排序，可以利用冒泡排序法
public static void sort(int data[]) {
for (int i = 0; i < data.length - 1; i++) {
for (int j = 0; j < data.length - 1 - i; j++) {
if (data[j] > data[j + 1]) {
int temp = 0;
temp = data[j];
data[j] = data[j + 1];
data[j + 1] = temp;
}
}
}
}
二分法具体步骤
public static int binarySearch(int[] data, int from, int to, int key) {
if (key > data[data.length - 1] || key < data[0]) {
return -1;
}
if (key == data[data.length - 1]) {
return data.length - 1;
}
if (key == data[0]) {
return 0;
}
if (from + 1 == to && (data[from] != key && data[to] != key)){
return -1;
}
int mid = (from + to ) / 2;
if (from < to) {
if (data[mid] == key) {
int temp = 1;
int mid1 = mid;
while(data[mid + 1] == key){
mid ++;
temp ++;
}
while(data[mid - temp] == key){
temp ++;
}
System.out.println("该数组中与所检索数相同数目为" + temp + "个");
return mid1;
} else if (key > data[mid]) {
return binarySearch(data, mid, to, key);
} else {
return binarySearch(data, from, mid, key);
}
}
return -1;
}
遍历打印输出方法
public static void printArray(int[] data) {
for (int i = 0; i < data.length; i++) {
System.out.print(data +" ");
}
}
}
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