[CareerCup][Google Interview] 打印最长序列

1. A
2. Ctrl+A
3. Ctrl+C
4. Ctrl+V

If you can only press the keyboard for N times (with the above four keys), please write a program to produce maximum numbers of A. If possible, please also print out the sequence of keys.

So the input parameter is N (No. of keys that you can press), the output is M (No. of As that you can produce).

 

这题又是一道经典的DP。打印这种类似最大结果的问题一般都会想到用DP

f[i][4]: 表示有四种方法,f[i][j] = max(f[i-1][k] + 各种操作)

如果要打印每个操作步骤,则要再设一个parent[i][j]数组,记录他的前任操作是哪个,然后递归调用。

 1 #include <iostream>
 2 using namespace std;
 3 
 4 int solve(int n)
 5 {
 6     int f[100][4];
 7 
 8     memset(f, 0, sizeof(f));
 9 
10     f[0][0] = 1;
11 
12     for(int i = 1; i < n; i++)
13         for(int j = 0; j < 4; j++)
14             for(int k = 0; k < 4; k++)
15             {
16                 if (j == 0) // add A
17                 {
18                     f[i][j] = max(f[i][j], f[i-1][k] + 1);
19                 }
20                 else if (j == 1) // ctrl+A
21                 {
22                     f[i][j] = max(f[i][j], f[i-1][k]);
23                 }
24                 else if (j == 2) // ctrl+C
25                 {
26                     if (k == 1) // only previous is ctrl+A makes ctrl+C available
27                         f[i][j] = max(f[i][j], f[i-1][k]);
28                 }
29                 else if (j == 3) //ctrl+V
30                 {
31                     if (k == 2)
32                         f[i][j] = max(f[i][j], f[i-1][k] * 2);
33                 }
34             }
35 
36     return max(f[n-1][3], f[n-1][0]);
37 }
38 
39 int main()
40 {
41     int N = 10;
42     cout << solve(N) << endl;
43 }
posted @ 2012-11-04 22:17  chkkch  阅读(447)  评论(1编辑  收藏  举报