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firstChar challenge

Posted on 2016-09-30
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Last Modified: 2016-10-06
Hi,

I am working on below challenge.

http://codingbat.com/prob/p168493

Given an array of non-empty strings, return a Map<String, String> with a key for every different first character seen, with the value of all the strings starting with that character appended together in the order they appear in the array.

firstChar(["salt", "tea", "soda", "toast"]) → {"t": "teatoast", "s": "saltsoda"}
firstChar(["aa", "bb", "cc", "aAA", "cCC", "d"]) → {"d": "d", "b": "bb", "c": "cccCC", "a": "aaaAA"}
firstChar([]) → {}

i was not clear on above description. please advise
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Question by:gudii9
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Expert Comment

by:tel2
ID: 41824327
Hi gudii9,

> "i was not clear on above description. please advise"

Unless you tell us which parts of the description you are not clear on, it's a bit hard for us to know how to advise you.  Do you expect us to rewrite the entire description and hope that you understand our version?

So, instead of making this a guessing game for us, please be specific.  We're expert programmers, not expert mind readers.

Thanks.
tel2
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Author Comment

by:gudii9
ID: 41826815

Given an array of non-empty strings, return a Map<String, String> with a key for every different first character seen, with the value of all the strings starting with that character appended together in the order they appear in the array.

firstChar(["salt", "tea", "soda", "toast"]) → {"t": "teatoast", "s": "saltsoda"}

why only character key s taken but not a/l/t in the salt??
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Expert Comment

by:phoffric
ID: 41826847
>> why only character key s taken but not a/l/t in the salt??

No particular reason. These challenges are sometimes testing your algorithm skills. In this case, the question is just testing your MAP and string skills. The question variants could have said take the first two chars for the key unless the third char (if it exists) is 'z', in which case "z" is the string key.

These questions are just exercises to make you stronger. But they may not have any value in professional programming on the job. (But making you stronger is, of course, very valuable - I am not saying that you should stop working these challenges.)
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Author Comment

by:gudii9
ID: 41826968
every different first

i missed first in description
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Author Comment

by:gudii9
ID: 41826988
let me think
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Author Comment

by:gudii9
ID: 41830626
public Map < String, String > firstChar(String[] strings) {

    Map < String, String > map = new HashMap < String, String > ();

    for (int i = 0; i < strings.length; i++) {

        String k = String.valueOf(strings[i].charAt(0));

        if (map.containsKey(k)) {
            String val = map.get(k) + strings[i];
            map.put(k, val);
        } else {
            map.put(k, strings[i]);
        }

    }
    return map;
}

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i pass all tests. any improvements or alternate approaches?
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Expert Comment

by:phoffric
ID: 41831025
Looks good. Maybe save a few keystrokes:
Map < String, String > map = new HashMap();
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Accepted Solution

by:
phoffric earned 500 total points
ID: 41831142
And, of course, as already explained in other questions, you can change the for-loop so that you do not need the counter, i.
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Author Comment

by:gudii9
ID: 41832124
public Map<String, String> firstChar(String[] strings) {
   
  Map<String, String> map = new HashMap();
   
 // for (int i = 0; i < strings.length; i++) {
 for(String str:strings)
     
    String k = String.valueOf(str.charAt(0));
     
    if (map.containsKey(k)) {
      String val = map.get(k) + strings[i];
      map.put(k, val);
    } else {
      map.put(k, strings[i]);
    }
     
  }
  return map;
}

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above gives below error
Compile problems:


Error:      String k = String.valueOf(str.charAt(0));
      ^^^^^^
Syntax error, insert "AssignmentOperator ArrayInitializer" to complete ArrayInitializerAssignement


see Example Code to help with compile problems

please advise
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Author Comment

by:gudii9
ID: 41832135
public Map<String, String> firstChar(String[] strings) {
   
  Map<String, String> map = new HashMap();
   
 // for (int i = 0; i < strings.length; i++) {
 for(String str:strings){
     
    String k = String.valueOf(str.charAt(0));
     
    if (map.containsKey(k)) {
      String val = map.get(k) + str;
      map.put(k, val);
    } else {
      map.put(k, str);
    }
     
  }
  return map;
}

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i corrected it. missed { and also used strings[i] at one place

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Expert Comment

by:phoffric
ID: 41832214
>> i corrected it.
Excellent!
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Expert Comment

by:phoffric
ID: 41832229
I am not against temporary variables, which good compilers will optimize away. And, when debugging a problem, temp variables are very helpful. But some projects hate them. So, if you see something like this, it is due to their hatred.
      // String val = map.get(k) + str;
      map.put(k, map.get(k) + str);

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Author Comment

by:gudii9
ID: 41832315
i see your point
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