A small error replace pi

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hey @arsh_goyal there are couple of small mistakes in your code

  1. you need to print results for each test case in new line so please write endl after printing a
  2. when you are replacing the characters of a[i+2] with a[i] you should start i from len not len -1 this way even the ‘\0’ end of string character would be replaced and no weird bugs would come.