1.3.cpp

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

string removeDuplicate1(string s)
{
    int check = 0;
    int len = s.length();
    if(len < 2) return s;
    string str = "";
    for(int i=0; i<len; ++i)
    {
        int v = (int)(s[i]-'a');
        if((check & (1<<v)) == 0)
        {
            str += s[i];
            check |= (1<<v);
        }
    }
    return str;
}

string removeDuplicate2(string s)
{
    int len = s.length();
    if(len < 2) return s;
    string str = "";
    for(int i=0; i<len; ++i)
    {
        if(s[i] != '\0')
        {
            str += s[i];
            for(int j=i+1; j<len; ++j)
                if(s[j]==s[i])
                    s[j] = '\0';
        }
    }
    return str;
}

void removeDuplicate3(char s[])
{
    int len = strlen(s);
    if(len < 2) return;
    int p = 0;
    for(int i=0; i<len; ++i)
    {
        if(s[i] != '\0')
        {
            s[p++] = s[i];
            for(int j=i+1; j<len; ++j)
                if(s[j]==s[i])
                    s[j] = '\0';
        }
    }
    s[p] = '\0';
}

void removeDuplicate4(char s[])
{
    int len = strlen(s);
    if(len < 2) return;
    bool c[256];
    memset(c, 0, sizeof(c));
    int p = 0;
    for(int i=0; i<len; ++i)
    {
        if(!c[s[i]])
        {
            s[p++] = s[i];
            c[s[i]] = true;
        }
    }
    s[p] = '\0';    
}

void removeDuplicate5(char s[])
{
    int len = strlen(s);
    if(len < 2) return;
    int check = 0, p = 0;
    for(int i=0; i<len; ++i)
    {
        int v = (int)(s[i]-'a');
        if((check & (1<<v))==0)
        {
            s[p++] = s[i];
            check |= (1<<v);
        }
    }
    s[p] = '\0';
}
int main()
{
    string s1 = "abcde";
    string s2 = "aaabbb";
    string s3 = "";
    string s4 = "abababc";
    string s5 = "ccccc";
    cout<<removeDuplicate1(s1)<<" "<<removeDuplicate2(s1)<<endl;
    cout<<removeDuplicate1(s2)<<" "<<removeDuplicate2(s2)<<endl;
    cout<<removeDuplicate1(s3)<<" "<<removeDuplicate2(s3)<<endl;
    cout<<removeDuplicate1(s4)<<" "<<removeDuplicate2(s4)<<endl;
    cout<<removeDuplicate1(s5)<<" "<<removeDuplicate2(s5)<<endl;
    char ss1[] = "abcde";
    char ss2[] = "aaabbb";
    char ss3[] = "";
    char ss4[] = "abababc";
    char ss5[] = "ccccc";
    removeDuplicate5(ss1);
    removeDuplicate5(ss2);
    removeDuplicate5(ss3);
    removeDuplicate5(ss4);
    removeDuplicate5(ss5);
    cout<<ss1<<" "<<ss2<<" "<<ss3<<" "<<ss4<<" "<<ss5<<endl;
    return 0;
}