CareerCup Find lexicographic minimum in a circular array 循环数组字典序

Write the code to find lexicographic minimum in a circular array, e.g. for the array 

 

BCABDADAB, the lexicographic mininum is ABBCABDAD

 

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It's a nice problem!

Here is a O(n) solution : 
We concat the string twice, then browse the string from left to right, 
keeping the the start position of the current answer seen so far. 
When we see a letter that would possibly be the start pos of a new answer, we do 
not update it yet, instead we keep an offset that defines the size of the prefix 
that has been checked for comparison of the current best answer and the possible 
new answer. 

 

#include<iostream>
#include<string>
 
std::string lex_min(const std::string&);
 
int main() {
    
    std::cout<<lex_min("BCDEBCDBCC");
    
    return 0;
}

std::string lex_min(const std::string& str) { 
    
    int size = str.size(); 
    std::string input = str + str; 
     
    int offset = 0; 
    int answer = -1; 
     
    for (int i = 0; i < size * 2; i++) { 
        if (answer == -1) 
        { 
            // First character 
            answer = i; 
        } 
        else if (input[i] < input[answer]) { 
            // We definitely have a new answer here 
            answer = i; 
            // Reset the offset for future tie 
            offset = 0; 
        } 
        else if (input[i] == input[answer + offset]) { 
            // We might have another answer here 
            // move the offset forward 
            offset++; 
        } 
        else if (input[i] < input[answer + offset]) { 
            // we have found something even better 
            // than what we had before 
            // Set marker for new answer 
            answer = i - offset; 
            offset = 0; 
            if(input[i] == input[answer]) /* THIS IS THE CORRECTION*/
                offset=1;
        } 
        else { 
            offset = 0; 
        } 
    } 
     
    return input.substr(answer, size); 
    
}