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count11 challenge

Posted on 2016-09-21
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Last Modified: 2016-09-22
Hi,

I am working on below challenge.
http://codingbat.com/prob/p167015
Psedo code:
1. check the array length 0  or 1 then retun 0
2.else if string does not consist of 11  return 0
3.else increment by 1 and calling same recursion function

I wrote my code as below and not passing all tests

public int count11(String str) {
  
  
  
 CharSequence cs1="11";
 
 //CharSequence cs2="aba";
  if(str.length()==0||str.length()==1||str.length()==2){
    return 0;
  }


  else if(!str.contains(cs1)){
    return 0;
  }
  else return 1+count11(str.substring(1));

}

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Expected      Run            
count11("11abc11") → 2      5      X      
count11("abc11x11x11") → 3      9      X      
count11("111") → 1      1      OK      
count11("1111") → 2      2      OK      
count11("1") → 0      0      OK      
count11("") → 0      0      OK      
count11("hi") → 0      0      OK      
count11("11x111x1111") → 4      9      X      
count11("1x111") → 1      3      X      
count11("1Hello1") → 0      0      OK      
count11("Hello") → 0      0      OK      
other tests
X      

Any improvements or alternate approaches?      

please advise
0
Comment
Question by:gudii9
  • 3
  • 3
6 Comments
 
LVL 37

Accepted Solution

by:
zzynx earned 500 total points
ID: 41810180
This works

public int count11(String str) {
  String string11 = "11";
 
  if(str.length()==0||str.length()==1){
    return 0;
  }

  if(str.startsWith(string11)){
     return 1 + count11(str.substring(2));
  }
  return count11(str.substring(1));
}

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0
 
LVL 7

Author Comment

by:gudii9
ID: 41810814
how contains different from startsWith method?
why cannot i use contains method here?
public int count11(String str) {
  
  
  
 CharSequence cs1="11";
 
 //CharSequence cs2="aba";
  if(str.length()<3){
    return 0;
  }


  else if(!str.contains(cs1)){
    return 0;
  }
  else return 1+count11(str.substring(2));

}

Open in new window


below also fails?
0
 
LVL 7

Author Comment

by:gudii9
ID: 41810929
public int count11(String str) {
  String string11 = "11";
 
  if(str.length()==0||str.length()==1){
    return 0;
  }

  if(str.startsWith(string11)){
     return 1 + count11(str.substring(2));
  }
  return count11(str.substring(1));
}

Open in new window


i like above approach checking if string 11 there then increment by 1 and shift two positions(as duplicats not needed) and call same recursion method
0
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LVL 37

Expert Comment

by:zzynx
ID: 41810962
>> i like above approach
OK. Good. :)

Again, you can of course replace
if(str.length()==0||str.length()==1){
    return 0;
}

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by
if(str.length()<2){
    return 0;
}

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>> why cannot i use contains method
contains() versus startsWith()
The answer is in their names.
0
 
LVL 7

Author Comment

by:gudii9
ID: 41811219
>> why cannot i use contains method
contains() versus startsWith()
The answer is in their names.

can you please elaborate.

one to check if starts with a string
other if contains only charactersequence?
0
 
LVL 37

Expert Comment

by:zzynx
ID: 41811979
Starting with a certain string
or
containing a certain string
are two different things.
In this case of recurrence you really need the first one
0

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