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 scratchimport 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：