前言
力扣都是力扣模式，而面试笔试会有acm模式，:older_man:不会，寄了
一些方法
hasNextXXX
- 会忽略空格
nextLine()
- 读取一整行，将\n前的内容全部返回
next()
读取下一个字符串，以空格为分隔
牛客上的练习
属于都是比较简单的，没涉及什么树啊链表什么的
A-A+B(1)
import java.util.Scanner;
public class Main{
public static void main(String[]args)
{
Scanner sc=new Scanner(System.in);
while(sc.hasNextInt())
{
int a=sc.nextInt();
int b=sc.nextInt();
System.out.println(a+b);
}
}
}B-A+B(2)
import java.util.Scanner;
public class Main
{
public static void main(String []args)
{
Scanner sc=new Scanner(System.in);
int count=sc.nextInt();
while(count>0)
{
int a=sc.nextInt();
int b=sc.nextInt();
System.out.println(a+b);
count--;
}
}
}C-A+B(3)
这题用nextLine()试试
import java.util.Scanner;
public class Main
{
public static void main(String []args)
{
Scanner sc=new Scanner(System.in);
while(sc.hasNextInt())
{
String[]nums=sc.nextLine().split(" ");
int a=Integer.parseInt(nums[0]);
int b=Integer.parseInt(nums[1]);
if(a==0||b==0)
{
break;
}
System.out.println(a+b);
}
}
}D-A+B(4)
import java.util.Scanner;
public class Main {
public static void main(String[]args)
{
Scanner sc=new Scanner(System.in);
while(sc.hasNextInt())
{
String[]nums=sc.nextLine().split(" ");
if(nums[0].equals("0"))
{
break;
}
int sum=0;
for(int i=1;i<nums.length;i++)
{
sum+=Integer.parseInt(nums[i]);
}
System.out.println(sum);
}
}
}E-A+B(5)
import java.util.Scanner;
public class Main {
public static void main(String []args)
{
Scanner sc=new Scanner(System.in);
int count=Integer.parseInt(sc.nextLine().split(" ")[0]);
while(count>0)
{
String[]nums=sc.nextLine().split(" ");
int sum=0;
for(int i=1;i<nums.length;i++)
{
sum+=Integer.parseInt(nums[i]);
}
System.out.println(sum);
count--;
}
}
} 一开始：
Scanner sc=new Scanner(System.in);
int count=sc.nextInt();
while(count>0)这就错了，因为nextInt()不会读取换行符
F-A+B(6)
import java.util.Scanner;
public class Main {
public static void main(String []args)
{
Scanner sc=new Scanner(System.in);
while(sc.hasNextLine())
{
String[]nums=sc.nextLine().split(" ");
int sum=0;
for(int i=1;i<nums.length;i++)
{
sum+=Integer.parseInt(nums[i]);
}
System.out.println(sum);
}
}
}H-字符串排序(1)
注意：Arrays在java.util.Arrays包内
import java.util.Scanner;
import java.util.Arrays;
public class Main
{
public static void main(String[]args)
{
Scanner sc=new Scanner(System.in);
sc.nextLine();
String []strs=sc.nextLine().split(" ");
Arrays.sort(strs);
for(String s:strs)
{
System.out.print(s+" ");
}
}
}I-字符串排序(2)
import java.util.Scanner;
import java.util.Arrays;
public class Main
{
public static void main(String []args)
{
Scanner sc=new Scanner(System.in);
while(sc.hasNextLine())
{
String[]strs=sc.nextLine().split(" ");
Arrays.sort(strs);
for(String s:strs)
{
System.out.print(s+" ");
}
System.out.println();
}
}
}树和链表
自己构造链表
以单链表反转为例子
注意事项
- 类都写在main类里
- 解决问题的方法单独一个函数
- 然后调用这个函数完输出就行了
import java.util.Scanner ;
public class Main
{
public static class Node
{
int val;
Node next;
public Node(){}
public Node(int val)
{
this.val=val;
}
}
public static void print(Node list)
{
StringBuilder sb=new StringBuilder();
while(list!=null)
{
sb.append(list.val).append(" ");
list=list.next;
}
System.out.println(sb.toString().trim());
}
public static Node reverseList(Node list)
{
Node pre=null;
Node cur=list;
while(cur!=null)
{
Node aft=cur.next;
cur.next=pre;
pre=cur;
cur=aft;
}
return pre;
}
public static void main(String []args)
{
Scanner sc=new Scanner(System.in);
while(sc.hasNextInt())
{
int n = sc.nextInt();
if (n == 0) {
System.out.println("list is empty");
continue;
}
Node list=new Node(sc.nextInt());
Node p=list;
for(int i=1;i<n;i++)
{
p.next=new Node(sc.nextInt());
p=p.next;
}
print(list);
list=reverseList(list);
print(list);
}
sc.close();
}
}自己构造树
题目页面 (kamacoder.com)
出生题目啊！
import java.util.HashMap;
import java.util.Scanner;
// Press Shift twice to open the Search Everywhere dialog and type `show whitespaces`,
// then press Enter. You can now see whitespace characters in your code.
public class Main {
private static HashMap<Character,Integer>mp;
private static int nodeIndex;
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);
while(sc.hasNextLine())
{
String[]strs=sc.nextLine().split(" ");
char[]preorder=strs[0].toCharArray();
char[]inorder=strs[1].toCharArray();
mp=new HashMap<>();
nodeIndex=0;
for(int i=0;i<preorder.length;i++)
{
mp.put(inorder[i],i);
}
TreeNode root=buildTree(preorder,inorder);
dfs(root);
System.out.println("");
}
}
public static class TreeNode
{
char val;
TreeNode left;
TreeNode right;
TreeNode(){}
TreeNode(char val)
{
this.val=val;
}
}
private static TreeNode buildTree(char[]preorder,char[]inorder)
{
int n=preorder.length;
return build(preorder,inorder,0,n-1);
}
private static TreeNode build(char[]preorder,char[]inorder,int l,int r)
{
int n=preorder.length;
if(nodeIndex>=n||l>r)return null;
char rootVal=preorder[nodeIndex];
TreeNode root=new TreeNode(rootVal);
++nodeIndex;
int mid=mp.get(rootVal);
root.left=build(preorder,inorder,l,mid-1);
root.right=build(preorder,inorder,mid+1,r);
return root;
}
private static void dfs(TreeNode node)
{
if(node==null)return;
dfs(node.left);
dfs(node.right);
System.out.print(node.val);
}
}题目页面 (kamacoder.com)
纯纯出生题目我操
import java.util.Arrays;
import java.util.HashMap;
import java.util.Scanner;
class TreeNode
{
int val;//当前位置
int letter;//字母标识
TreeNode left;//左右节点
TreeNode right;
TreeNode() {}
TreeNode(int val) { this.val = val; }
TreeNode(int val,int letter) {
this.val = val;
this.letter = letter;
}
TreeNode(int val, TreeNode left, TreeNode right) {
this.val = val;
this.left = left;
this.right = right;
}
}
public class Main {
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);
int n=sc.nextInt();//node个数
sc.nextLine();
HashMap<Integer,TreeNode>mp=new HashMap<>();
String[][]str=new String[n+1][3];
boolean []isRoot=new boolean[n+1];//是否是root
Arrays.fill(isRoot,true);
for(int i=1;i<=n;i++)
{
str[i]=sc.nextLine().split(" ");//按行分割放到矩阵里
TreeNode node = new TreeNode(i, (int)str[i][0].charAt(0) - 'A');
mp.put(i,node);//第一轮将val和node的对应关系放到map里
}
TreeNode root=null;
for(int i=1;i<=n;i++)
{
TreeNode node=mp.get(i);
if(str[i][1].equals("0"))
{
node.left=null;
}else
{
int left=Integer.parseInt(str[i][1]);
node.left=mp.get(left);
isRoot[left]=false;
}
if(str[i][2].equals("0"))
{
node.right=null;
}else
{
int right=Integer.parseInt(str[i][2]);
node.right=mp.get(right);
isRoot[right]=false;
}
}
for(int i=1;i<=n;i++)
{
if(isRoot[i]==true)
{
root=mp.get(i);
break;
}
}
preOrder(root);
System.out.println();
inOrder(root);
System.out.println();
postOrder(root);
System.out.println();
}
public static void preOrder(TreeNode root){//前序遍历
if(root != null){
System.out.print((char)(root.letter + 'A'));
preOrder(root.left);
preOrder(root.right);
}
}
public static void inOrder(TreeNode root){//中序遍历
if(root != null){
inOrder(root.left);
System.out.print((char)(root.letter + 'A'));
inOrder(root.right);
}
}
public static void postOrder(TreeNode root){//后序遍历
if(root != null){
postOrder(root.left);
postOrder(root.right);
System.out.print((char)(root.letter + 'A'));
}
}
}
