leetcode/1844-replace-all-digits-with-characters/1844-replace-all-digits-with-characters.c

char * replaceDigits(char * s){
    int len = strlen(s);
    for (int i = 1; i < len; i += 2) {
        s[i] = s[i - 1] + (s[i] - '0');
    }
    return s;
}