小红书3.26Java后端笔试全AC分享

第一题：解密字符串，模拟一下即可，每个字符往前数三个

import java.util.*;

public class Main {
    private static String getRes(String s) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < s.length(); ++i) {
            char ch = s.charAt(i);
            sb.append((char) ((ch - 'a' - 3 + 26) % 26 + 'a'));
        }
        return sb.toString();
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        String s = in.next();
        System.out.println(getRes(s));
    }
}

第二题：K排序，其实就是模拟一下链表的操作。判断每相邻两个整数（n-1和n，如1和2）的相对顺序，如果顺序不对则进行一次操作。最后把这些操作按至多k个一组看能分多少组。

import java.util.*;

public class Main {
    private static int getRes(int n, int k, int[] nums) {
        Map<Integer, Integer> rec = new HashMap<>();
        for (int i = 0; i < n; ++i) rec.put(nums[i], i);
        int res = 0;
        for (int i = 1; i < n; ++i) if (rec.get(i + 1) < rec.get(i)) rec.put(i + 1, n + (res++));
        return res / k + (res % k == 0 ? 0 : 1);
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int t = in.nextInt();
        while (t-- > 0) {
            int n = in.nextInt(), k = in.nextInt();
            int[] nums = new int[n];
            for (int i = 0; i < n; ++i) nums[i] = in.nextInt();
            System.out.println(getRes(n, k, nums));
        }
    }
}

第三题：染色。这里本来以为是差分数组或者类似线段树之类的题，结果暴力直接AC？？后来就没细想，可以在评论区讨论讨论。

import java.util.*;

public class Main {
    private static long[] getRes(int n, long[] nums, int m, int[][] opidxs, String ops, long[] params) {
        for (int i = 0; i < m; ++i) {
            char op = ops.charAt(i);
            int left = opidxs[i][0] - 1, right = opidxs[i][1] - 1;
            long param = params[i];
            if (op == '|') for (int j = left; j < n && j <= right; ++j) nums[j] = nums[j] | param;
            else if (op == '&') for (int j = left; j < n && j <= right; ++j) nums[j] = nums[j] & param;
            else for (int j = left; j < n && j <= right; ++j) nums[j] = param;
        }
        return nums;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        long[] nums = new long[n];
        for (int i = 0; i < n; ++i) nums[i] = in.nextLong();
        int m = in.nextInt();
        int[][] opidxs = new int[m][2];
        for (int i = 0; i < m; ++i) opidxs[i][0] = in.nextInt();
        for (int i = 0; i < m; ++i) opidxs[i][1] = in.nextInt();
        String ops = in.next();
        long[] params = new long[m];
        for (int i = 0; i < m; ++i) params[i] = in.nextLong();
        long[] res = getRes(n, nums, m, opidxs, ops, params);
        for (int i = 0; i < n; ++i) {
            System.out.print(res[i]);
            if (i != n - 1) System.out.print(' ');
            else System.out.print('\n');
        }
    }
}