微软2017校招编程题 Composition(DP)

题目来源：
https://hihocoder.com/contest/mstest2016oct/problem/2
描述
Alice writes an English composition with a length of N characters. However, her teacher requires that M illegal pairs of characters cannot be adjacent, and if 'ab' cannot be adjacent, 'ba' cannot be adjacent either.
In order to meet the requirements, Alice needs to delete some characters.
Please work out the minimum number of characters that need to be deleted.
输入
The first line contains the length of the composition N.
The second line contains N characters, which make up the composition. Each character belongs to 'a'..'z'.
The third line contains the number of illegal pairs M.
Each of the next M lines contains two characters ch1 and ch2,which cannot be adjacent.  
For 20% of the data: 1 ≤ N ≤ 10
For 50% of the data: 1 ≤ N ≤ 1000  
For 100% of the data: 1 ≤ N ≤ 100000, M ≤ 200.
输出
One line with an integer indicating the minimum number of characters that need to be deleted.
样例提示
Delete 'a' and 'd'.
样例输入
5
abcde
3
ac
ab
de
样例输出
2

思路

题意：给出一个长度为n(n<100000)的只包含小写字符的字符串s[0...n-1]，再给出m(m<=200)个字符对（如：ab），表示ab和ba不能出现在串中（后文称这个不能出现的集合为黑名单。问最少删除几个字符能够使得输入串是合法的？

http://blog.youkuaiyun.com/raalghul/article/details/52782731

http://blog.youkuaiyun.com/dumeichen/article/details/52785133

dp[N][26]：对于当前位置，以某字符结尾的最长长度。采用更省空间的dp[26]

代码

见思路中参考网址