VAPI01  Vitaliy and Pie
After a hard day Vitaly got very hungry and he wants to eat his favorite potato pie. But it's not that simple. Vitaly is in the first room of the house with n room located in a line and numbered starting from one from left to right. You can go from the first room to the second room, from the second room to the third room and so on — you can go from the (n  1)th room to the nth room. Thus, you can go to room xonly from room x  1.
The potato pie is located in the nth room and Vitaly needs to go there.
Each pair of consecutive rooms has a door between them. In order to go to room x from room x  1, you need to open the door between the rooms with the corresponding key.
In total the house has several types of doors (represented by uppercase Latin letters) and several types of keys (represented by lowercase Latin letters). The key of type t can open the door of type T if and only if t and T are the same letter, written in different cases. For example, key f can open door F.
Each of the first n  1 rooms contains exactly one key of some type that Vitaly can use to get to next rooms. Once the door is open with some key, Vitaly won't get the key from the keyhole but he will immediately run into the next room. In other words, each key can open no more than one door.
Vitaly realizes that he may end up in some room without the key that opens the door to the next room. Before the start his run for the potato pie Vitaly can buy any number of keys of any type that is guaranteed to get to room n.
Given the plan of the house, Vitaly wants to know what is the minimum number of keys he needs to buy to surely get to the room n, which has a delicious potato pie. Write a program that will help Vitaly find out this number.
Input
The zeroth line contain an integer t  testcases
The first line of the input contains a positive integer n (2 ≤ n ≤ 105) — the number of rooms in the house.
The second line of the input contains string s of length 2·n  2. Let's number the elements of the string from left to right, starting from one.
The odd positions in the given string s contain lowercase Latin letters — the types of the keys that lie in the corresponding rooms. Thus, each odd position i of the given string s contains a lowercase Latin letter — the type of the key that lies in room number (i + 1) / 2.
The even positions in the given string contain uppercase Latin letters — the types of doors between the rooms. Thus, each even position iof the given string s contains an uppercase letter — the type of the door that leads from room i / 2 to room i / 2 + 1.
Output
Print the only integer — the minimum number of keys that Vitaly needs to buy to surely get from room one to room n.Example
Sample:
Input:
1
3
aAbB
Output:
0
hide comments
ponnamtharun:
20190407 11:24:00
use simple hashing technique


rahulrex1998:
20190110 17:56:07
if you are using STL then don't forget to clear it. 

malcolm123_ssj:
20181011 09:46:09
use map :p


arnav_agyeya:
20170826 13:31:14
solution in O(nlog(n)) sould be more than enough for this question. 

kaushalag29:
20170516 17:26:46
Got AC but still not satisfied..


Devashish Mathur:
20151225 11:13:08
easy 

xpshekhar:
20151225 02:26:53
good one


loverboy:
20150921 20:02:01
AC in 1 go..... nice question only use logic 

Addy:
20150910 07:11:10
requires some brainstorming! Best Of Luck! :) 

rahul2907:
20150902 00:10:57
easy :P :D

Added by:  _R0bb_ 
Date:  20150507 
Time limit:  0.100s 
Source limit:  12345B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ASM64 JSMONKEY SCM qobi SCM guile 