Java经典基础练习31-40

【程序31】

题目：将一个数组逆序输出。

[java] view plain copy print?import java.util.*;
public class lianxi31 {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
int a[] = new int[20];
System.out.println(”请输入多个正整数（输入-1表示结束）：”);
int i=0,j;
do{
a[i]=s.nextInt();
i++;
}while (a[i-1]!=-1);
System.out.println(”你输入的数组为：”);
for( j=0; j<i-1; j++) {
System.out.print(a[j]+” ”);
}
System.out.println(”\n数组逆序输出为：”);
for( j=i-2; j>=0; j=j-1) {
System.out.print(a[j]+” ”);
}
<span style=”white-space:pre”> </span>}
}

import java.util.*;
public class lianxi31 {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
int a[] = new int[20];
System.out.println("请输入多个正整数（输入-1表示结束）：");
int i=0,j;
do{
a[i]=s.nextInt();
i++;
}while (a[i-1]!=-1);
System.out.println("你输入的数组为：");
for( j=0; j<i-1; j++) {
System.out.print(a[j]+"   ");
}
System.out.println("\n数组逆序输出为：");
for( j=i-2; j>=0; j=j-1) {
System.out.print(a[j]+"   ");
}
<span style="white-space:pre">    </span>}
}

【程序32】

题目：取一个整数a从右端开始的4～7位。

[java] view plain copy print?import java.util.*;
public class lianxi32 {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
System.out.print(”请输入一个7位以上的正整数：”);
long a = s.nextLong();
String ss = Long.toString(a);
char[] ch = ss.toCharArray();
int j=ch.length;
if (j<7){System.out.println(“输入错误！”);}
else {
System.out.println(”截取从右端开始的4～7位是：”+ch[j-7]+ch[j-6]+ch[j-5]+ch[j-4]);
}
}
}

import java.util.*;
public class lianxi32 {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
System.out.print("请输入一个7位以上的正整数：");
long a = s.nextLong();
String ss = Long.toString(a);
char[] ch = ss.toCharArray()
4000
;
int j=ch.length;
if (j<7){System.out.println("输入错误！");}
else {
System.out.println("截取从右端开始的4～7位是："+ch[j-7]+ch[j-6]+ch[j-5]+ch[j-4]);
}
}
}

【程序33】

题目：打印出杨辉三角形（要求打印出10行如下图）

1

1 1

1 2 1

1 3 3 1

1 4 6 4 1

1 5 10 10 5 1

…………

[java] view plain copy print?public class lianxi33 {
public static void main(String[] args) {
int[][] a = new int[10][10];
for (int i = 0; i < 10; i++) {
a[i][i] = 1;
a[i][0] = 1;
}
for (int i = 2; i < 10; i++) {
for (int j = 1; j < i; j++) {
a[i][j] = a[i - 1][j - 1] + a[i - 1][j];
}
}
for (int i = 0; i < 10; i++) {
for (int k = 0; k < 2 * (10 - i) - 1; k++) {
System.out.print(” ”);
}
for (int j = 0; j <= i; j++) {
System.out.print(a[i][j] + ” ”);
}
System.out.println();
}
}
}

public class lianxi33 {
public static void main(String[] args) {
int[][] a = new int[10][10];
for (int i = 0; i < 10; i++) {
a[i][i] = 1;
a[i][0] = 1;
}
for (int i = 2; i < 10; i++) {
for (int j = 1; j < i; j++) {
a[i][j] = a[i - 1][j - 1] + a[i - 1][j];
}
}
for (int i = 0; i < 10; i++) {
for (int k = 0; k < 2 * (10 - i) - 1; k++) {
System.out.print(" ");
}
for (int j = 0; j <= i; j++) {
System.out.print(a[i][j] + "   ");
}
System.out.println();
}
}
}

【程序34】

题目：输入3个数a,b,c，按大小顺序输出。

[java] view plain copy print?import java.util.Scanner;

public class lianxi34 {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
System.out.println(”请输入3个整数：”);
int a = s.nextInt();
int b = s.nextInt();
int c = s.nextInt();
if (a < b) {
int t = a;
a = b;
b = t;
}
if (a < c) {
int t = a;
a = c;
c = t;
}
if (b < c) {
int t = b;
b = c;
c = t;
}
System.out.println(”从大到小的顺序输出:”);
System.out.println(a + ” ” + b + “ ” + c);
}
}

import java.util.Scanner;

public class lianxi34 {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
System.out.println("请输入3个整数：");
int a = s.nextInt();
int b = s.nextInt();
int c = s.nextInt();
if (a < b) {
int t = a;
a = b;
b = t;
}
if (a < c) {
int t = a;
a = c;
c = t;
}
if (b < c) {
int t = b;
b = c;
c = t;
}
System.out.println("从大到小的顺序输出:");
System.out.println(a + " " + b + " " + c);
}
}

【程序35】

题目：输入数组，最大的与第一个元素交换，最小的与最后一个元素交换，输出数组。

[java] view plain copy print?import java.util.*;
public class lianxi35 {
public static void main(String[] args) {
int N = 8;
int[] a = new int
;
Scanner s = new Scanner(System.in);
int idx1 = 0, idx2 = 0;
System.out.println(”请输入8个整数：”);
for(int i=0; i<N; i++) {
a[i] = s.nextInt();
}
System.out.println(”你输入的数组为：”);
for(int i=0; i<N; i++) {
System.out.print(a[i] + ” ”);
}
12f46

int max =a[0], min = a[0];
for(int i=0; i<N; i++) {
if(a[i] > max) {
max = a[i];
idx1 = i;
}
if(a[i] < min) {
min = a[i];
idx2 = i;
}
}
if(idx1 != 0) {
int temp = a[0];
a[0] = a[idx1];
a[idx1] = temp;
}
if(idx2 != N-1) {
int temp = a[N-1];
a[N-1] = a[idx2];
a[idx2] = temp;
}
System.out.println(”\n交换后的数组为：”);
for(int i=0; i<N; i++) {
System.out.print(a[i] + ” ”);
}
}
}

import java.util.*;
public class lianxi35 {
public static void main(String[] args) {
int N = 8;
int[] a = new int
;
Scanner s = new Scanner(System.in);
int idx1 = 0, idx2 = 0;
System.out.println("请输入8个整数：");
for(int i=0; i<N; i++) {
a[i] = s.nextInt();
}
System.out.println("你输入的数组为：");
for(int i=0; i<N; i++) {
System.out.print(a[i] + " ");
}
int max =a[0], min = a[0];
for(int i=0; i<N; i++) {
if(a[i] > max) {
max = a[i];
idx1 = i;
}
if(a[i] < min) {
min = a[i];
idx2 = i;
}
}
if(idx1 != 0) {
int temp = a[0];
a[0] = a[idx1];
a[idx1] = temp;
}
if(idx2 != N-1) {
int temp = a[N-1];
a[N-1] = a[idx2];
a[idx2] = temp;
}
System.out.println("\n交换后的数组为：");
for(int i=0; i<N; i++) {
System.out.print(a[i] + " ");
}
}
}

【程序36】

题目：有n个整数，使其前面各数顺序向后移m个位置，最后m个数变成最前面的m个数

[java] view plain copy print?import java.util.Scanner;

public class lianxi36 {
public static void main(String[] args) {
int N = 10;
int[] a = new int
;
Scanner s = new Scanner(System.in);
System.out.println(”请输入10个整数：”);
for (int i = 0; i < N; i++) {
a[i] = s.nextInt();
}
System.out.print(”你输入的数组为：”);
for (int i = 0; i < N; i++) {
System.out.print(a[i] + ” ”);
}
System.out.print(”\n请输入向后移动的位数：”);
int m = s.nextInt();
int[] b = new int[m];
for (int i = 0; i < m; i++) {
b[i] = a[N - m + i];
}
for (int i = N - 1; i >= m; i–) {
a[i] = a[i - m];
}
for (int i = 0; i < m; i++) {
a[i] = b[i];
}
System.out.print(”位移后的数组是：”);
for (int i = 0; i < N; i++) {
System.out.print(a[i] + ” ”);
}
}
}

import java.util.Scanner;

public class lianxi36 {
public static void main(String[] args) {
int N = 10;
int[] a = new int
;
Scanner s = new Scanner(System.in);
System.out.println("请输入10个整数：");
for (int i = 0; i < N; i++) {
a[i] = s.nextInt();
}
System.out.print("你输入的数组为：");
for (int i = 0; i < N; i++) {
System.out.print(a[i] + " ");
}
System.out.print("\n请输入向后移动的位数：");
int m = s.nextInt();
int[] b = new int[m];
for (int i = 0; i < m; i++) {
b[i] = a[N - m + i];
}
for (int i = N - 1; i >= m; i--) {
a[i] = a[i - m];
}
for (int i = 0; i < m; i++) {
a[i] = b[i];
}
System.out.print("位移后的数组是：");
for (int i = 0; i < N; i++) {
System.out.print(a[i] + " ");
}
}
}

【程序37】

题目：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。

[java] view plain copy print?import java.util.Scanner;

public class lianxi37 {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
System.out.print(”请输入排成一圈的人数：”);
int n = s.nextInt();
boolean[] arr = new boolean
;
for (int i = 0; i < arr.length; i++) {
arr[i] = true;
}
int leftCount = n;
int countNum = 0;
int index = 0;
while (leftCount > 1) {
if (arr[index] == true) {
countNum++;
if (countNum == 3) {
countNum = 0;
arr[index] = false;
leftCount–;
}
}
index++;
if (index == n) {
index = 0;
}
}
for (int i = 0; i < n; i++) {
if (arr[i] == true) {
System.out.println(”原排在第” + (i + 1) + “位的人留下了。”);
}
}
}
}

import java.util.Scanner;

public class lianxi37 {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
System.out.print("请输入排成一圈的人数：");
int n = s.nextInt();
boolean[] arr = new boolean
;
for (int i = 0; i < arr.length; i++) {
arr[i] = true;
}
int leftCount = n;
int countNum = 0;
int index = 0;
while (leftCount > 1) {
if (arr[index] == true) {
countNum++;
if (countNum == 3) {
countNum = 0;
arr[index] = false;
leftCount--;
}
}
index++;
if (index == n) {
index = 0;
}
}
for (int i = 0; i < n; i++) {
if (arr[i] == true) {
System.out.println("原排在第" + (i + 1) + "位的人留下了。");
}
}
}
}

【程序38】

题目：写一个函数，求一个字符串的长度，在main函数中输入字符串，并输出其长度。

/*………………

*……题目意思似乎不能用length()函数 */

不用函数做不出

【程序39】

题目：编写一个函数，输入n为偶数时，调用函数求1/2+1/4+…+1/n,当输入n为奇数时，调用函数1/1+1/3+…+1/n(利用指针函数)

//没有利用指针函数

[java] view plain copy print?import java.util.*;

public class lianxi39 {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
System.out.print(”请输入一个正整数 n= ”);
int n = s.nextInt();
System.out.println(”相应数列的和为：” + sum(n));
}

public static double sum(int n) {
double res = 0;
if (n % 2 == 0) {
for (int i = 2; i <= n; i += 2) {
res += (double) 1 / i;
}
} else {
for (int i = 1; i <= n; i += 2) {
res += (double) 1 / i;
}
}
return res;
}
}

import java.util.*;

public class lianxi39 {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
System.out.print("请输入一个正整数 n= ");
int n = s.nextInt();
System.out.println("相应数列的和为：" + sum(n));
}

public static double sum(int n) {
double res = 0;
if (n % 2 == 0) {
for (int i = 2; i <= n; i += 2) {
res += (double) 1 / i;
}
} else {
for (int i = 1; i <= n; i += 2) {
res += (double) 1 / i;
}
}
return res;
}
}

【程序40】

题目：字符串排序。

[java] view plain copy print?public class lianxi40 {
public static void main(String[] args) {
int N = 5;
String temp = null;
String[] s = new String
;
s[0] = “matter”;
s[1] = “state”;
s[2] = “solid”;
s[3] = “liquid”;
s[4] = “gas”;
for (int i = 0; i < N; i++) {
for (int j = i + 1; j < N; j++) {
if (compare(s[i], s[j]) == false) {
temp = s[i];
s[i] = s[j];
s[j] = temp;
}
}
}
for (int i = 0; i < N; i++) {
System.out.println(s[i]);
}
}

static boolean compare(String s1, String s2) {
boolean result = true;
for (int i = 0; i < s1.length() && i < s2.length(); i++) {
if (s1.charAt(i) > s2.charAt(i)) {
result = false;
break;
} else if (s1.charAt(i) < s2.charAt(i)) {
result = true;
break;
} else {
if (s1.length() < s2.length()) {
result = true;
} else {
result = false;
}
}
}
return result;
}
}

public class lianxi40 {
public static void main(String[] args) {
int N = 5;
String temp = null;
String[] s = new String
;
s[0] = "matter";
s[1] = "state";
s[2] = "solid";
s[3] = "liquid";
s[4] = "gas";
for (int i = 0; i < N; i++) {
for (int j = i + 1; j < N; j++) {
if (compare(s[i], s[j]) == false) {
temp = s[i];
s[i] = s[j];
s[j] = temp;
}
}
}
for (int i = 0; i < N; i++) {
System.out.println(s[i]);
}
}

static boolean compare(String s1, String s2) {
boolean result = true;
for (int i = 0; i < s1.length() && i < s2.length(); i++) {
if (s1.charAt(i) > s2.charAt(i)) {
result = false;
break;
} else if (s1.charAt(i) < s2.charAt(i)) {
result = true;
break;
} else {
if (s1.length() < s2.length()) {
result = true;
} else {
result = false;
}
}
}
return result;
}
}