java - Create a String from chars at indexes 0, 1, 4, 5, 8, 9 -

i have came across problem on codingbat.com:

given string, return string made of chars @ indexes 0,1, 4,5, 8,9 ... "kittens" yields "kien".

here code:

public string altpairs(string str) {    string result = "";    (int = 0; < str.length(); i++) {     result += str.substring(i, i+1);      if (i > 0 && str.indexof(str.substring(i, i+1)) % 2 != 0) += 2;   }    return result; } 

for "codinghorror", should return "congrr".

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• why code return "congrro" parameter "codinghorror"?

it solved in simpler way:

string result = "";  (int = 0; < str.length(); += 4) { result += str.substring(i, math.min(str.length(), + 2));           }  return result; 

more:

• it's bad idea change counter variable inside for loop - use while loop then.
• substring(int beginindex, int endindex) - endindex exclusive.