Broken Keyboard

 

Broken Keyboard

Time Limit:1000MS  Memory Limit:65536K
Total Submit:48 Accepted:15

Description

Bruce Force's keyboard is broken, only a few keys are still working. Bruce has figured out he can still type texts by switching the keyboard layout whenever he needs to type a letter which is currently not mapped to any of the m working keys of the keyboard.

You are given a text that Bruce wishes to type, and he asks you if you can tell him the maximum number of consecutive characters in the text which can be typed without having to switch the keyboard layout. For simplicity, we assume that each key of the keyboard will be mapped to exactly one character, and it is not possible to type other characters by combination of different keys. This means that Bruce wants to know the length of the largest substring of the text which consists of at most m different characters.

Input

The input contains several test cases, each test case consisting of two lines. The first line of each test case contains the number m (1 ≤ m ≤ 128), which specifies how many keys on the keyboard are still working. The second line of each test case contains the text which Bruce wants to type. You may assume that the length of this text does not exceed 1 million characters. Note that the input may contain space characters, which should be handled like any other character.

The last test case is followed by a line containing one zero.

Output

For each test case, print one line with the length of the largest substring of the text which consists of at most m different characters.

Sample Input

5

This can't be solved by brute force.

1

Mississippi

0

 

 

Sample Output

7

2

 

 

Source

本以为用map会快一点，却发现这是行不通的。

以下是多次超时的代码:

 

#include <iostream>
#include  <map>
using namespace  std;

const int N = 1000005 ;

int  main()
{
    char str[N];
    map<char, int> mm;
    int k;
    int s, e, len, maxlen;
    while(cin>>k && k)
    {
        getchar();
        cin.getline(str,N,'\n');
        //================================
        len = strlen(str);
        mm.clear();
        s = 0;
        for(e = 0; e < len && mm.size() < k; e++)
            if(mm[str[e]])
                mm[str[e]] ++;
            else
                mm[str[e]] = 1;
        if(e >= len)
        {
            cout<<len<<endl;
            continue;
        }
        maxlen = e - s;
        //====================================
        for(; e < len; e++)
        {
            if(mm[str[e]])
            {
                mm[str[e]]++;
                cout<<e<<" "<<s<<endl;
                if(e - s > maxlen)
                {
                    
                    maxlen = e - s;
                }
            }
            else
            {
                while(1)
                {
                    if(mm[str[s]] > 1)
                        mm[str[s]]--;
                    else
                        break;
                    s++;
                }
                mm.erase(str[s]);
                mm[str[e]] = 1;
                s++;
            }
        }
        cout<<maxlen + 1<<endl;
    }
    return 0;
}

 

把map丢去后，自己写的hash，就过了

 

//28111 Xredman 1257 Accepted 1260K 62MS C++ 1.0K 2009-03-28 20:30:58.0 
#include <iostream>
using namespace  std;

const int N = 1000005 ;

int mm[500 ];

int  main()
{
    char str[N];
    int k;
    int s, e, len, maxlen,cc;
    while(cin>>k && k)
    {
        getchar();
        cin.getline(str,N,'\n');
        //================================
        len = strlen(str);
        for(s = 0; s < 500; s++)
            mm[s] = 0;
        s = 0;
        cc = 0;
        for(e = 0; e < len && cc < k; e++)
            if(mm[str[e]])
                mm[str[e]]++;
            else
            {
                mm[str[e]] = 1;
                cc++;
            }
        if(e >= len)
        {
            cout<<len<<endl;
            continue;
        }
        maxlen = e - s;
        //====================================
        for(; e < len; e++)
        {
            if(mm[str[e]])
            {
                mm[str[e]]++;
                if(e - s > maxlen)
                {
                    
                    maxlen = e - s;
                }
            }
            else
            {
                while(1)
                {
                    if(mm[str[s]] > 1)
                        mm[str[s]]--;
                    else
                        break;
                    s++;
                }
                mm[str[s]] = 0;
                mm[str[e]] = 1;
                s++;
            }
        }
        cout<<maxlen + 1<<endl;
    }
    return 0;
}