求字符串最长不含重复字符的子串长度

趋势科技的笔试题(CSDN)

#include <cstring>
#include <cstdlib>
/*
令appear所有元素置为-1;
1. diff = i-appear[str[i]];
2. arrCnt[i] = arrCnt[i-1]+1;   (arrCnt[i-1] < diff)
             = diff             (arrCnt[i-1] >= diff)
3. appear[str[i]]=i;
4. goto 1;

*/
int max_unique_substr(char * str)
{    
    int len = (int)strlen(str);
    int appear[256]={0};
    memset(appear,-1,sizeof(appear));
    int preCnt=1;
    appear[str[0]]=0;
    int ret = 1;    
    for(int i=1;i<len;++i)
    {
        int dif = i-appear[str[i]];
        if(dif>preCnt)
        {
            ++preCnt;
            if(preCnt>ret)
            {
                ret = preCnt;
            }

        }
        else
        {
            preCnt = dif;
        }
        appear[str[i]] = i;
    }
    return ret;
}