cracking the coding interview 5th 1.5

gistfile1.txt

1.5 Implement a method to perform basic string compression using the counts of repeated characters. For example, the string aabcccccaaa would become a2blc5a3. If the "compressed" string would not become smaller than the original string, your method should return the original string.

extra memory : none
Time complxity : O(n)
잘못된 입력은 없다고 가정.
test case : "", "a", "abc", "abbcc", "aabcc", "aabbc", "aaaaa"
test case 작성 기준 :빈문자열, 한글자, 모두 동일 substring, 1글자 짜리 substring의 위치(첫,중앙,끝), 나머지는 다 동일.

string compressStr(string input) {
    int length = input.length();
    string output =""; 
    char c = input[0];
    int index = 0;
    
    if(length <= 0) return ""; //or throw 처리 
    
    for(int i=0 ; i<length ; i++) {
        if(input[i] == c) {
            index++;  
        } else {
            output += (c + to_string(index));
            index = 1;
            c = input[i];
        }
    }
    
    output += (c + to_string(index));
    
    if(output.length() >= input.length()) return input;
    else return output;
}