java写的常见算法

一些我们的教科书上的常用算法考试，这些可能也会出现在面试中，所以自己花了一些时间整理了一下，程序全部通过执行，有的鲁棒性可能还不够好，希望大家可以添加一些常用的算法，自己以后还会进一步添加。

package Algorithm;import java.util.Scanner;public class Test {public static void main(String[] args) {//testBonus();//perSqrt();//selectSort();//statistics();//gcdAndLcm1();//prime(124);//Sum20();//classSum();//positiveIntegerLengthAndConverse();/*while(true) {palindrom();}*///intercept();//count3Quit();//selectFun(3);peachCount();}//海滩上有一堆桃子，五只猴子来分。第一只猴子把这堆桃子平均分成5份，多了一个，这只猴子吃了多的一个桃子，拿走了一份。//第二只猴子把剩下的桃子又平均分成五份，又多了一个，它同样吃了多的拿走了一份，第三、第四、第五只猴子都是这样，问海滩上原来最少有多少个桃子？public static void peachCount() {int n = count(1);System.out.println(n);}public static int count(int n) {if(n==5) return 6;return 5*count(n+1)+1;}//编写一个函数，输入n为偶数时，调用函数1/2+1/4+...+1/n,当输入n为奇数时，调用函数1/1+1/3+...+1/n;public static void selectFun(int n) {float sum = 0f;float temp = 0f;for(;n>0;n=n-2) {temp = (float)1/n;sum += temp; }System.out.println(sum);}//有n个人围成一圈，顺序排号，从第一个人开始报数（从1到3报数）凡报到3的人退出圈子，问最后留下的是原来第几号的那位public static void count3Quit() {System.out.println("请输入人数：");Scanner scan = new Scanner(System.in);int n = scan.nextInt();boolean[] b = new boolean[n];for(int i=0;i<b.length;i++) {b[i] = true;}int cout = 0;int leftCount = n;int index = 0;while(leftCount>1) {if(b[index]) {cout++;if(cout==3) {cout = 0;b[index] = false;leftCount--;}}index++;if(index==n) {index = 0;}}for(int i=0;i<n;i++) {if(b[i]) {System.out.println(i+1);}}}/*数三减一(利用java类的实现)public class Count3Quit {public static void main(String []args) {KidCircle kc = new KidCircle(500);int countNum = 0;Kid k = kc.first;while(kc.count>1) {countNum++;if(countNum==3) {countNum = 0;kc.delete(k);}k = k.right;}System.out.println(kc.first.id);}}class Kid {int id;Kid left;Kid right;}class KidCircle {int count = 0;Kid first,last;KidCircle(int n){for(int i=0;i<n;i++) {add();}}void add() {Kid k = new Kid();k.id = count;if(count==0) {first = k;last = k;k.left = k;k.right = k;}else{last.right = k;k.left = last;k.right = first;first.left = k;last = k;}count++;}void delete(Kid k) {if(count<=0) return;else if(count == 1) {first = last = null;}else {k.left.right = k.right;k.right.left = k.left;if(k==first) {first = k.right;}if(k==last) {last = k.left;}}count--;}}*///取一个整数a从右端开始的4~7位。public static void intercept() {int a = 0;long b = 18745678;a = (int)Math.floor(b%Math.pow(10, 7)/Math.pow(10, 3));System.out.println(a);}//一个五位数，判断它是不是回文数。即12321是回文数，个位和万位相同，十位和千位相同public static void palindrom() {System.out.println("请输入一个五位的回文数：");Scanner scan = new Scanner(System.in);long l = scan.nextLong();if(l<10000||l>99999) {System.out.println("请输入正确的回文数！");return;}int a[] = new int[5];int b[] = new int[5];boolean is = false;for(int i=4;i>=0;i--) {a[i] = (int)l/(int)Math.pow(10, i);l = l%(int)Math.pow(10, i);}for(int i=0;i<=4;i++) {b[i] = a[i];}for(int i=0,j=4;i<5;i++,j--) {if(a[i]!=b[j]) {is = false;break;}else {is = true;}}if(is) {System.out.println("is a Palindrom!");}else {System.out.println("is not a Palindrom!");}}//给一个不多于5位数的正整数，要求：一 求它是几位数 二 逆序打印出各位数字public static void positiveIntegerLengthAndConverse() {Scanner scan = new Scanner(System.in);long lvalue = scan.nextLong();if(lvalue<0||lvalue>=100000) {System.out.println("请输入不大于五位的整数！");System.exit(0);}String str  = lvalue +"";int length = str.length();char[] c = str.toCharArray();System.out.println(lvalue+"是"+length+"位数；");System.out.print("逆序打印为：");for(int i=c.length-1;i>=0;i--) {System.out.print(c[i]+" ");}}//求1+2!+3!+...+20!//这种情况下用循环比用递归的效率要高很多public static void classSum() {long sum=0;long fac=1;for(int i=1;i<=3;i++) {fac = fac*i;sum +=fac;}System.out.println("20的阶层和为："+sum);}//有一分数序列：2/1,3/2,5/3,8/5,13/8,21/13...求出这个数列的前20项之和public static void Sum20() {float a,b,c,t,sum;a = 1;b = 2;sum = 0;for(int i=0;i<20;i++) {c = b/a;sum += c;t = a;a = b;b = t+b;}System.out.println(""+sum);}//两个乒乓球队进行比赛，各出三人。甲队为啊a,b,c三人，乙队为x,y,z三人。//已抽签决定比赛名单。有人向队员打听比赛的名单。a说他不和x比，c说他不和x,z比，请编程打出三队赛手的名单。//思想：定义一个类，三个成员变量abc，然后根据xyz初始化这个类，循环满足条件的都放入ArrayList中，在输出；//将一个正整数分解质因子。例如：124=2*2*31。public static void prime(int n) {for(int i=2;i<=n/2;i++) {if(n%i==0) {System.out.print(i+"*");prime(n/i);}}System.out.print(n);System.exit(0);}//输入两个正整数，求其最大公约数和最小公倍数//利用斩除法（欧几里德算法）//写法1public static void gcdAndLcm1() {System.out.println("请输入两个整数：");Scanner scan = new Scanner(System.in);int a = scan.nextInt();int b = scan.nextInt();int a1 = a;int b1 = b;while(true) {if((a=a%b)==0) {System.out.println("最大公约数：" +b+"\n最小公倍数："+a1*b1/b);return;}if((b=b%a)==0) {System.out.println("最大公约数：" +a+"\n最小公倍数："+a1*b1/a);return;}}}//写法2public static void gcdAndLcm() {System.out.println("请输入两个整数：");Scanner scan = new Scanner(System.in);int a = scan.nextInt();int b = scan.nextInt();int a1 = a;int b1 = b;int temp,t;if(a<b) {temp = a;a = b;b = temp;}if(b==0) {System.out.println("除数不能为0");return;}while(a%b!=0) {t = a%b;a=b;b=t;}System.out.println("最大公约数：" +b+"\n最小公倍数："+a1*b1/b);}//输入一行字符，分别统计出其中英文字母、空格、数字和其他字符的个数public static void statistics() {System.out.println("请输入字符串：");Scanner scan = new Scanner(System.in);String str = scan.nextLine();String e1 = "[a-zA-Z]";String e2 = " ";String e3 = "[0-9]";int letterCount = 0;int spaceCount = 0;int digitalCount = 0;int otherCount = 0;char[] c = str.toCharArray();String[] arrStr  = new String[c.length];for(int i=0;i<c.length;i++) {arrStr[i] = String.valueOf(c[i]);}for(int i=0;i<arrStr.length;i++) {if(arrStr[i].matches(e1)) {letterCount++;}else if(arrStr[i].matches(e2)) {spaceCount++;}else if(arrStr[i].matches(e3)) {digitalCount++;}else{otherCount++;}}System.out.println("英文字母："+letterCount+"\n空格："+spaceCount+"\n数字："+digitalCount+"\n其他:"+otherCount);}//插入排序/*int []a = {1,4,2,7,5,9,98,-2,7979,6,987};insertSort(a);for(int i=0;i<a.length;i++) {System.out.print(a[i]+" ");}*/public static void insertSort(int[]a) {int length = a.length;int i,j;for(i=1;i<length;i++) {j = a[i];while(i>0&&j<a[i-1]) {a[i] = a[i-1];i--;}a[i] = j;}}//排序public static void selectSort() {System.out.println("请输入三个数：\n");Scanner scan = new Scanner(System.in);int i = scan.nextInt();int j = scan.nextInt();int z = scan.nextInt();int l = i;if(i>j){l = i;i=j;j= l;}if(i>z){l = i;i=z;z= l;}if(j>z){l = z;z=j;j= l;}System.out.println(i+"," +j+","+z +"");}//完全平方public static void perSqrt() {long k = 0;for(k=1;k<1000000L;k++) {if((Math.floor(Math.sqrt(k+100))==Math.sqrt(k+100))&&(Math.floor(Math.sqrt(k+168))==Math.sqrt(k+168))) {System.out.println(k);}}}//求利润public static void testBonus(){System.out.println("请输入利润（万元）：");Scanner scan = new Scanner(System.in);Double p = scan.nextDouble();Double bonus = 0.0;if(p<=10){bonus = p*0.1;}else if(p<20) {bonus = 10*0.1 + (p-10)*0.075;}else if(p<40) {bonus = 10*0.1 + 10*0.075 + (p-20)*0.05;}else if(p<60) {bonus = 10*0.1 + 10*0.075 + 20*0.05 + (p-40)*0.03;}else if(p<=100) {bonus = 10*0.1 + 10*0.075 + 20*0.05 + 20*0.03 + (p-60)*0.015;}else {bonus = 10*0.1 + 10*0.075 + 20*0.05 + 20*0.03 + 40*0.015 +(p-100)*0.01;}System.out.println(bonus);}//直接插入排序                    //运行结果：2 3 5 9 12 34 67 75 100 public static void insertSort(int[]a,int n) {int temp;for(int i=2;i<n;i++) {temp = a[i];int j=i-1;for(;a[j]>temp;j--) {a[j+1] = a[j];}a[j+1] = temp;}}//希尔排序//这个排序写了很久,i必须是++，这样便于后面的遍历public static void shellSort(int[]a,int n) {int i,j,d,temp;d=n/2;while(d>0) {for(i=d;i<n;i++) {                     j=i-d;for(;j>=0&&a[j]>a[j+d];j=j-d) {temp = a[j];a[j] = a[j+d];a[j+d] = temp;}}d=d/2;}}//冒泡排序public static void bubbleSort(int[]a,int n) {int i,j,temp;for(i=n;i>0;i--) {for(j=0;j<i-1;j++) {if(a[j]>a[j+1]) {temp = a[j];a[j] = a[j+1];a[j+1] = temp;}}}}//快速排序//一定要加上j>i&&，不然没结果public static void quickSort(int[]a,int s,int t) {int i,j,temp;i=s;j=t;if(i<j) {temp = a[i];while(i!=j) {while(j>i&&a[j]>temp) j--;if(i<j){a[i]=a[j];i++;}while(j>i&&a[i]<temp) i++;if(i<j){a[j]=a[i];j--;}}a[i] = temp;quickSort(a,s,i-1);quickSort(a,i+1,t);}}}