面经笔记

Posted 2020-08-14 太空工程车

1. 

输入一串用空格隔开的数字串，对于数字串的奇数位按升序排序，偶数位按降序排序。

示例输入：

4 6 2 3 6 7 8 1

处理过程：

奇数位：4 2 6 8 升序排序结果： 2 4 6 8

偶数位：6 3 7 1 降序排序结果： 7 6 3 1

结果输出：2 7 4 6 6 3 8 1

 1 import java.util.ArrayList;
 2 import java.util.PriorityQueue;
 3 import java.util.Scanner;
 4 
 5 /**
 6  * Created by Mingxiao on 10/14/2016.
 7  * Time: O(N*logN)
 8  * Space: O(N)
 9  */
10 public class Main {
11 
12     public int[] sort(int[] arr) {
13         if (arr == null || arr.length <= 1) {
14             return arr;
15         }
16 
17         PriorityQueue<Integer> increaseQueue = new PriorityQueue<>();
18         PriorityQueue<Integer> decreaseQueue = new PriorityQueue<>();
19         int[] result = new int[arr.length];
20 
21         int oddIndex = 1;
22         int evenIndex = 0;
23 
24         while (oddIndex < arr.length) {
25             decreaseQueue.offer(arr[oddIndex]);
26             increaseQueue.offer(arr[evenIndex]);
27 
28             oddIndex += 2;
29             evenIndex += 2;
30         }
31 
32         oddIndex -= 2;
33         evenIndex = 0;
34 
35         while (evenIndex < arr.length && oddIndex > 0) {
36             result[evenIndex] = increaseQueue.poll();
37             result[oddIndex] = decreaseQueue.poll();
38             evenIndex += 2;
39             oddIndex -= 2;
40         }
41 
42         return result;
43     }
44 
45     public static void main(String[] args) {
46 
47         Scanner cin = new Scanner(System.in);
48         ArrayList<Integer> list = new ArrayList<>();
49         while (cin.hasNext()) {
50             list.add(cin.nextInt());
51         }
52 
53 
54         int[] testArr = new int[list.size()];
55         for (int i = 0; i < list.size(); i++) {
56             testArr[i] = list.get(i);
57         }
58         int[] result = new Main().sort(testArr);
59         for (int i = 0; i < result.length; i++) {
60             System.out.print(result[i] + ", ");
61         }
62     }
63 }

2.

某个字符串只存在三种格式字符分别是0~9、A~Z和a~z，请按照数字在前、大写字母次之、小写字母最后的方式排序，字符串长度不超过100。

例如：CBA321zyx

        123ABCxyz

 1 import java.util.Scanner;
 2 
 3 /**
 4  * Created by Mingxiao on 10/14/2016.
 5  * Time: O(N)
 6  * Space: O(N)
 7  */
 8 public class Main {
 9 
10     public static String sort(String str) {
11         char[] sortArr = new char[128];
12         StringBuilder sb = new StringBuilder();
13 
14         for (int i = 0; i < str.length(); i++) {
15             sortArr[str.charAt(i) - 0]++;
16         }
17 
18         for (int i = 48; i < sortArr.length; i++) {
19             if (sortArr[i] != 0) {
20                 char temp = (char)i;
21                 for (int j = 0; j < sortArr[i]; j++) {
22                     sb.append(temp);
23                 }
24             }
25         }
26 
27         return sb.toString();
28     }
29 
30 
31     public static void main(String[] args) {
32 
33         Scanner cin = new Scanner(System.in);
34         String str = "";
35         while (cin.hasNext()) {
36             str = cin.nextLine();
37         }
38 
39         System.out.print(sort(str));
40     }
41 }

 3. 

给出两个字串A，B。将A字串转化为B字串，转化一共有两种方式:删除连续的n个字符，一次操作费用为2。增加连续的n个字符(增加的字符是什么由你决定)，一次操作费用为n+2。求把A变为B最小费用。

dsafsadfadf -> fdfd : 7
aaaaaaaa -> bbbbbbbb: 12
提示：
"dsafsadfadf" 变成 "fdfd" 最少的代价的一种方法是：
1. "dsafsadfadf" -> "f" 删除连续的10个，代价2
2. "f" -> "fdfd" 增加连续的3个（”dfd”），代价为3 ＋ 2 ＝ 5
总共的最小代价为2 ＋ 5 ＝ 7，其他方法的代价都不小于7
"aaaaaaaa" 变成 “bbbbbbbb” 最小代价的一种方法是：
1. "aaaaaaaa" 全部删除，代价2
2. 增加8个连续的‘b‘，代价10
总共的最小代价为2 ＋ 10 ＝ 12
注意，有些最优的方案可能要做多次的删除和增加操作，不限于两次。

 1 import java.util.Scanner;
 2 
 3 /**
 4  * Created by Mingxiao on 10/14/2016.
 5  * dp
 6  * Time: O(N^3)
 7  */
 8 public class Main {
 9 
10     private static final int BOUND = 2000;
11     private static final int INF = Integer.MAX_VALUE;
12 
13     public static int minCost(String a, String b) {
14         int l1 = a.length();
15         int l2 = b.length();
16         int[][] first = new int[BOUND][BOUND];
17         int[][] second = new int[BOUND][BOUND];
18         int[][] third = new int[BOUND][BOUND];
19 
20         for (int i = 0; i <= l1; i++) {
21             first[0][i] = 2; second[0][i] = third[0][i] = INF;
22         }
23         for (int i = 0; i <= l2; i++) {
24             second[i][0] = i + 2; first[i][0] = third[i][0] = INF;
25         }
26         third[0][0] = 0;
27         for (int j = 1; j <= l2; j++) {
28             for (int i = 1; i <= l1; i++) {
29                 third[j][i] = a.charAt(i - 1) == b.charAt(j - 1) ? Math.min(Math.min(third[j - 1][i - 1], second[j - 1][i - 1]), first[j - 1][i - 1]) : INF;
30                 second[j][i] = first[j][i] = INF;
31                 for (int k = 1; k <= j; k++) {
32                     second[j][i] = Math.min(second[j][i], Math.min(second[j - k][i] + k, Math.min(first[j - k][i] + k + 2, third[j - k][i] + k + 2)));
33                 }
34                 for (int k = 1; k <= i; k++) {
35                     first[j][i] = Math.min(first[j][i], Math.min(first[j][i - k], Math.min(second[j][i - k] + 2, third[j][i - k] + 2)));
36                 }
37             }
38         }
39         return Math.min(Math.min(third[l2][l1], second[l2][l1]), first[l2][l1]);
40     }
41 
42     public static void main(String[] args) {
43 
44         int counter = 0;
45 
46         Scanner cin = new Scanner(System.in);
47         if (cin.hasNext()) {
48             counter = cin.nextInt();
49         }
50 
51         String[] strArr = new String[counter * 2];
52         int index = 0;
53         while (cin.hasNext()) {
54             strArr[index] = cin.nextLine();
55         }
56 
57         for (int i = 0; i < strArr.length; i++) {
58             System.out.println(minCost(strArr[i],strArr[++i]));
59         }
60 
61     }
62 }