They Are Everywhere
Contest: Codeforces Round 364 (Div. 2)
Difficulty rating: 1500
Tags: binary search, strings, two pointers

Sergei B., the young coach of Pokemons, has found the big house which consists of n flats ordered in a row from left to right. It is possible to enter each flat from the street. It is possible to go out from each flat. Also, each flat is connected with the flat to the left and the flat to the right. Flat number 1 is only connected with the flat number 2 and the flat number n is only connected with the flat number n - 1.

There is exactly one Pokemon of some type in each of these flats. Sergei B. asked residents of the house to let him enter their flats in order to catch Pokemons. After consulting the residents of the house decided to let Sergei B. enter one flat from the street, visit several flats and then go out from some flat. But they won't let him visit the same flat more than once.

Sergei B. was very pleased, and now he wants to visit as few flats as possible in order to collect Pokemons of all types that appear in this house. Your task is to help him and determine this minimum number of flats he has to visit.

Input format:
The first line contains the integer n (1 ≤ n ≤ 100 000) — the number of flats in the house.

The second line contains the row s with the length n, it consists of uppercase and lowercase letters of English alphabet, the i-th letter equals the type of Pokemon, which is in the flat number i.

Output format:
Print the minimum number of flats which Sergei B. should visit in order to catch Pokemons of all types which there are in the house.

Constraints:
Time limit: 2.0 s
Memory limit: 256.0 MB

Note:
In the first test Sergei B. can begin, for example, from the flat number 1 and end in the flat number 2.

In the second test Sergei B. can begin, for example, from the flat number 4 and end in the flat number 6.

In the third test Sergei B. must begin from the flat number 2 and end in the flat number 6.

Example input:
3
AaA

Example output:
2

Example input:
7
bcAAcbc

Example output:
3

Editorial:
At first let's find all different letters, which exist in the given string. It can be done with help of the array with letters or with help of the set. Then we need to use the array len, where len[i] equals to minimal length of the substring, which ends in the position i and contains all different letters from the given string. If for some position i there is no such a substring, we will store in the len[i] some big number, which more than the length of the given string, for example, 109.
Now we need to iterate through all different letters of the string in any order. Let the current letter equals to c. Let's iterate on the positions of the given string from the left to the right and will store in the variable last the last position of the string s in which s[last] = c. At first last =  - 1. Let the current position of the given string equals to i. If s[i] = c we need to make last = i. If for current position i the value of the last equals to  - 1 we need to make len[i] = 109 (because there is no substring which ends in the position i and contains all different letters of the given string s). In the other case, we need to update len[i] = max(len[i], i - last + 1).
The answer is the minimal value from all values of the array len after we iterated through all different letters of the given string s.