2021 阿里巴巴编程题

import java.util.*;
import java.lang.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int t = sc.nextInt();
        for (int k = 0; k < t; k++) {
            int n = sc.nextInt();
            int[][] nums = new int[n][2];
            for (int i = 0; i < n; i++) {
                nums[i][0] = sc.nextInt();
            }
            for (int i = 0; i < n; i++) {
                nums[i][1] = sc.nextInt();
            }
            Arrays.sort(nums, (o1, o2) -> o1[0]==o2[0]? o2[1]-o1[1]:o1[0]-o2[0]);

            System.out.println(solve(nums));
        }
    }
    
    public static int solve(int[][] nums) {
        int n = nums.length;
        int[] dp = new int[n+1];    // dp[i]表示长度为i的LIS子序列最后一位的值
        int maxLen = 1;
        dp[1] = nums[0][1];
        for (int i = 1; i < n; i++) {
            if (nums[i][1] > dp[maxLen]) {
                maxLen++;
                dp[maxLen] = nums[i][1];
            } else {
                int idx = find(dp, maxLen, nums[i][1]);
                dp[idx] = nums[i][1];
            }
        }
        return maxLen;
    }
    
    // >=
    public static int find(int[] dp, int maxLen, int target) {
        int left = 1, right = maxLen;
        while (left <= right) {
            int mid = left + ((right - left) >> 1);
            if (dp[mid] < target) {
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }
        return left;
    }
}

https://www.nowcoder.com/test/question/a55198d2e65746009110226f2f6c8533?pid=30440638&tid=52108831

 

 

import java.util.*;
import java.lang.*;

public class Main {
    static int[][] dirs = {{1,0}, {-1,0}, {0,1}, {0,-1}};
    static class node {
        int x, y, cnt, used;
        node(int xx, int yy, int count, int num) {
            x = xx; y = yy; cnt = count; used = num;
        }
    }
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        char[][] board = new char[n][m];
        int sx = 0, sy = 0, ex = 0, ey = 0;
        for (int i = 0; i < n; i++) {
            String row = sc.next();　　// 注意：不要用nextLine，next只取到有效字符
            for (int j = 0; j < row.length(); j++) {
                board[i][j] = row.charAt(j);
                if (board[i][j] == 'S') {
                    sx = i; sy = j;
                }
                if (board[i][j] == 'E') {
                    ex = i; ey = j;
                }
            }
        }
        int[][] vis = new int[n][m];
        Deque<node> que = new LinkedList<>();
        que.offer(new node(sx, sy, 0, 5));
        vis[sx][sy] = 1;
        boolean flag = false;;
        while (!que.isEmpty()) {
            node cur = que.poll();
            if (cur.x == ex && cur.y == ey) {
                System.out.println(cur.cnt);
                flag = true;
                break;
            }
            for (int[] dir: dirs) {
                int xx = cur.x + dir[0], yy = cur.y + dir[1];
                if (!inBoard(n, m, xx, yy) || board[xx][yy] == '#' || vis[xx][yy] == 1) continue;
                que.offer(new node(xx, yy, cur.cnt + 1, cur.used));
                vis[xx][yy] = 1;
            }
            // 中心对称
            int x1 = n -1 - cur.x, y1 = m - 1 - cur.y;
            if (cur.used > 0 && inBoard(n, m, x1, y1) && board[x1][y1] != '#' && vis[x1][y1] == 0) {
                que.offer(new node(x1, y1, cur.cnt + 1, cur.used-1));
                vis[x1][y1] = 1;
            }
        }
        if (!flag) System.out.println(-1);
    }
    public static boolean inBoard(int n, int m, int x, int y) {
        if (x < 0 || x >= n || y < 0 || y >= m) return false;
        return true;
    }
}

https://blog.csdn.net/qq_37702890/article/details/122846069?utm_medium=distribute.pc_relevant.none-task-blog-2~default~baidujs_title~default-0.pc_relevant_paycolumn_v3&spm=1001.2101.3001.4242.1&utm_relevant_index=2

 

有个物品可供选择，必须选择其中个物品，请按字典序顺序输出所有选取方案的物品编号

与与等被认为是同一种方案，输出字典序最小的即可

import java.util.*;
// dfs
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();

        List<Integer> path = new ArrayList<>(m);
        dfs(path, n, m, 1, 0);   
    }
    
    public static void dfs(List<Integer> path, int n, int m, int index, int count) {
        if (count == m) {
            for (int i = 0; i < m; i++) {
                if (i != 0) System.out.print(" ");
                System.out.print(path.get(i));
            }
            System.out.println();
            return ;
        }
        
        if (index > n) return ;
        // 选择当前的数字
        for (int i = index; i <= n; i++) {
            path.add(i);
            count++;
            dfs(path, n, m, i+1, count);   
            path.remove(path.size() - 1);
            count--;   
        }
    }
}

　　

 

关于BufferedReader

import java.util.*;
import java.io.*;
public class Main {
    public static void main(String[] args) throws Exception{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int T = Integer.parseInt(br.readLine());
        while (T-- > 0) {
            int n = Integer.parseInt(br.readLine());
            String[] params = br.readLine().trim().split(" ");
            int[] costs = new int[n];
            for (int i = 0; i < n; i++) costs[i] = Integer.parseInt(params[i]);
            Arrays.sort(costs);
            int ans = 0;
            while (n >= 4) {
                // 方案1. 最轻的人每次带一个让人过去； 方案2. 最轻的人和次最轻的人过去，最轻的人过来，最重和次重过去，次轻过来
                ans += Math.min(2 * costs[0] + costs[n-1] + costs[n-2], costs[0] + 2*costs[1] + costs[n-1]);
                n -= 2;
            }
            if (n == 3) {
                ans += costs[0] + costs[1] + costs[2];
            } else {
                ans += costs[1];
            }
            System.out.println(ans);
        }
    }
}