Educational Codeforces Round 32 Problem 888C - K-Dominant Character

1) Link to the problem: http://codeforces.com/contest/888/problem/C

2) Description: 

You are given a string s consisting of lowercase Latin letters. Character c is called k-dominant if each substring of s with length at least k contains this character c.

You have to find minimum k such that there exists at least one k-dominant character.

Input

The first line contains string s consisting of lowercase Latin letters (1 ≤ |s| ≤ 100000).

Output

Print one number — the minimum value of k such that there exists at least one k-dominant character.

 

3) 思路：

这题的tag居然是binary search，我做的时候基本没往这方面想。

我的思路就是算每个字母的maxgap然后求最小。

数据长度最长是10^5，然后26个字母注意：大小写要区分。

最后大概是O(n)左右，time limit是2s。所以肯定能过。O(n^2)的话就不用想了，O(n^2)属于不理智行为。

4) Code：

#include <iostream>
#include <cstring>
using namespace std;
int main(){
    string s;
    cin>>s;
    int n = s.size();
    int min = INT_MAX;

    for(int i = 0; i < 52; i++)
    {
        char c;
        if(i<26)
            c = (char)('a' + i);
        else
            c = (char)('A' + i - 26);

        int count = 0;
        int maxgap = 0;
        for(int j = 0; j < n; j++){
            if(s[j] == c) 
            {
                if(maxgap < count)
                    maxgap = count;
                count = 0;
            }
            else {
                count ++;
            }
        }
        if(maxgap < count)
            maxgap = count;
        if(maxgap < min)
            min = maxgap;
        if(min==0)
            break;
    }
    cout << min + 1;
    return 0;
}