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Determine if there are duplicate characters in the string

1. Question: Is the ASCII string or Unicode string, if the ASCII string can only have 256 characters, when the length of the string exceeds 256, there must be repeated characters

2. Determine if there are any characters appearing two times

#include <iostream>
#include <string>
#include <memory.h>
using namespace Std;
BOOL IsUnique (String str)
{
if (Str.length () >256)
return false;
BOOL isexist[256];
memset (Isexist,false, sizeof (isexist));
int count=0;
for (int i=0;i<str.length (); i++)
{
int val=str[i];
if (Isexist[val])
{
return false;
}
Else
{
Isexist[val]=true;
cout<<val<<endl;
cout<<str[i]<<endl;

}

}
return true;
}
int main ()
{
String str= "abc";
BOOL Isnodup;
Isnodup=isunique (str);
if (isnodup)
cout<< "No DUP" <<endl;
Else
cout<< "DUP" <<endl;
return 0;

}

Or, with the displacement method, which one appears each time is set to 1 (with the number of displacements expressed). With the number of displacements before and if there is repetition with the result greater than 0.

However, consider how many bits the data type corresponds to, assuming that the int type (32-bit) can only be used to contain characters less than 32 bits, assuming only lowercase ' a '-' Z '.

BOOL IsUnique2 (String str) {    if (str.length () >26)        return false;    int checker=0;    for (int i=0;i<str.length (); i++)    {        int val=str[i]-' a ';        cout<<val<<endl;            if ((checker& (1<<val)) >0)                return false;            Checker |= (1<<val);  cout<<checker<<endl;    }    return true;}

There are other solutions, such as whether check each character is duplicated, but with a high degree of time complexity.

C + + Learning