hackerrank Java Data Structures

地址：https://www.hackerrank.com/domains/java/java-data-structure

题目https://www.hackerrank.com/challenges/java-list

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    public static void main(String[] args) {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        LinkedList<Integer> l = new LinkedList<Integer>();
        for(int i = 0;i < n;i++)
            l.add(in.nextInt());
        int q = in.nextInt();
        while(q-- > 0){
            String op = in.next();
            if(op.equals("Insert")){
                int x = in.nextInt(),y = in.nextInt();
                l.add(x,y);
            }
            else{
                int x = in.nextInt();
                l.remove(x);
            }
        }
        for(int x : l)
            System.out.print(x + " ");  
    }
}

题目：https://www.hackerrank.com/challenges/phone-book
题意：使用map
思路：以前好像没怎么用过.nextLine()
.nextLine()用来读入一行数据，这个和C++已经取消的gets相似，都会读入换行，如果使用前有读入数据的话，提前读入空行.nextLine() 防止影响后面的读入。
代码：

//Complete this code or write your own from scratch
import java.util.*;
import java.io.*;

class Solution{
   public static void main(String []argh)
   {
      Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        in.nextLine();
        HashMap<String,Integer> mp = new HashMap<String,Integer>();
        while(n-- > 0){
            String name = in.nextLine();
            int number = in.nextInt();
            mp.put(name, number);
            in.nextLine();
        }
        while(in.hasNext()){
            String name = in.nextLine();
            if(mp.containsKey(name))
                System.out.println(name + "=" + mp.get(name));
            else
                System.out.println("Not found");
        }
   }
}

题目：https://www.hackerrank.com/challenges/java-stack/problem
代码：

import java.util.*;
class Solution{

   public static void main(String []argh)
   {
      Scanner in = new Scanner(System.in);
        while(in.hasNext()){
            String s = in.next();
            Stack<Character> st = new Stack<Character>();
            for(int i = 0;i < s.length();i++){
                if(!st.empty()){
                    switch(s.charAt(i)){
                    case ')':
                        if(st.peek() == '(')
                            st.pop();
                        break;
                    case ']':
                        if(st.peek() == '[')
                            st.pop();
                        break;
                    case '}':
                        if(st.peek() == '{')
                            st.pop();
                        break;
                    default:
                        st.push(s.charAt(i));
                    }
                }
                else
                    st.push(s.charAt(i));
            }
            if(st.empty())
                System.out.println("true");
            else
                System.out.println("false");
        }
   }
}

题目：https://www.hackerrank.com/challenges/java-hashset/problem
代码：