[算法]求一段包含所有种类的字符子串

#include <cstring>int foo(const char* str, int m, int n){
    int hit[256], count = 0, begin = 0, end, len = m;
    memset(hit,0,256*4);
    int j;
    for(j = 0; j < m && count < n; ++j){
        if(1 == ++hit[str[j]]){
            ++count;
        }
    }
    len = j;
    end = j;
    int i = 0;
    while(i < m-1){
        while(n == count && i < m-1){
            if(0 == --hit[str[i++]]){
                --count;
            }
        }
        if( n != count && len > end - (i-1)){
            begin = i-1;
            len = end - (i-1);        
        }
        for(j = end; count != n; ++j){
            if(1 == ++hit[str[j%m]]){
                ++count;
                end = j+1;
                if(j-i+1 < len){
                    begin = i;
                    len = j-i+1;
                }
            }
        }
    } 
    return len;
}