"Sword Point offer": [55] The first non-repeating character in a character stream

Title: Implement a function to find the first character in a character stream that appears only once. For example, when you read only the first two characters "go" from a character stream, the first character that appears only once is "G". When the first six characters "Google" are read from the stream, the character that appears only once is "L".
This is similar to the character in [35] where the first occurrence of the string is found. So the detailed process is not mentioned here.
Scenario One: Sequential scan. time Complexity O (n*n) + spatial Complexity O (N). After sequential scanning, record the number of occurrences of each character. Then the sequential scan array gets the first number of characters corresponding to 1.
Scenario Two: Hash table method. time complexity O (n) + spatial complexity 0 (N)-hash table. The method mentioned in [35] above is: Use the hash table to record the number of each character, using ASCII as the key value of the hash table, and the number of occurrences of the character as the hash table value. This problem is also used in a hash table to record, ASCII as the key value of the hash table, the position of the character corresponding to, also can be understood as subscript as the value of the hash table. For example, the array is initialized to-1, the first character that appears is 0, the second one appears is 1 ... Once again, if it appears again, set to-2, and at the end of the search, look for the first number equal to 0.
The following code is primarily used to simulate character stream manipulation using strings.
The specific implementation code is:

#include <iostream>using namespace Std;int index=0;int occurrence[256];void ReSet () {for (int i=0;i<256;i++) Occurrence[i]=-1;index=1;} void InSert (char *str) {while (*str!= ') {if (occurrence[*str]==-1) occurrence[*str]=index;//first appears; else if ( occurrence[*str]>=0) occurrence[*str]=2;//appear here; str++;}} Char firstapperance (char *str) {char ch= ' + '; while (*str!= '} ') {if (occurrence[*str]==1) {Ch=*str;return ch;} str++;} return ch;} int main () {char *strr[3]={"abcdabc", "ABCABC", "abc"};for (int i=0;i<3;i++) {ReSet (); InSert (Strr[i]);//read in character; char Result=firstapperance (Strr[i]); if (Result! = ') cout<<strr[i]<< ": The first occurrence of the character is:" <<result< <endl;elsecout<<strr[i]<< ": The character in the string does not appear once! "<<endl;} System ("pause"); return 0;}

Operation Result:

"Sword Point offer": [55] The first non-repeating character in a character stream