import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String str = in.nextLine();
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextInt()) { // 注意 while 处理多个 case
            int a = in.nextInt();
            int b = in.nextInt();
            System.out.println(a + b);
        }
    }
}

ACM模式模版

模版来源

public class Main {

    public static void main(String[] args) {
        //1.数据输入
        Scanner in = new Scanner(System.in);
        //读数字
        int numLen = in.nextInt();
        int[] numArr = new int[numLen];
        int i = 0;
        while(in.hasNextInt() && i < numLen){
            numArr[i] = in.nextInt();
            i++;
        }
        //读字符串
        int strLen = in.nextInt();
        in.nextLine(); //数字到字符串要换行
        String[] strArr = new String[strLen];
        //或者 strArr[] = in.nextLine().split(" ");
        int j = 0;
        while(in.hasNextLine() && j < strLen){
            strArr[j] = in.nextLine();
            j++;
        }
        
        //2. 处理
        Solution solution = new Solution();
        String result = solution.process(numArr, strArr);
        
        //3. 输出
        System.out.println(result);
        //四舍五入输出小数
        String str = String.format("%.2f",3.555);
        System.out.println(str);
    }
}

//下面类似 LeetCode 的核心代码模式
class Solution {
    public String process(int[] nums, String[] strs) {
        StringBuilder sb = new StringBuilder();
        sb.append(Arrays.toString(nums));
        sb.append(" && ");
        sb.append(Arrays.toString(strs));
        return sb.toString();
    }
}

ACM模式下建立二叉树

package lc114_;

import java.util.*;

class TreeNode {
    TreeNode left, right;
    int val;

    public TreeNode(int val) {
        this.val = val;
    }
}

public class Solution {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String[] input = in.nextLine().split(",");
        Integer[] output = new Integer[input.length];
        for (int i = 0; i < input.length; i++) {
            // 重点
            if(input[i].equals("null")) {
                output[i] = null;
            }else{
                output[i] = Integer.parseInt(input[i]);
            }
        }

        LinkedList<Integer> inputList = new LinkedList<>(Arrays.asList(output));
        TreeNode treeNode = buildTree(inputList);
        System.out.println(preorderTraversal(treeNode));
    }

    public static TreeNode buildTree(LinkedList<Integer> inputList){
        TreeNode node = null;
        if (inputList ==null || inputList.isEmpty()){
            return null;
        }
        Integer data = inputList.removeFirst();
        if (data != null){
            node = new TreeNode(data);
            node.left = buildTree(inputList);
            node.right = buildTree(inputList);
        }
        return node;
    }

    public static List<Integer> preorderTraversal(TreeNode root) {
        List<Integer> result = new ArrayList<>();
        preorder(root, result);
        return result;
    }

    public static void preorder(TreeNode root, List<Integer> result) {
        if (root == null) {
            return;
        }
        result.add(root.val);
        preorder(root.left, result);
        preorder(root.right, result);
    }
}