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55// Time: O(N), Space: O(N)
class Solution {
public String reformat(String s) {
StringBuilder letters=new StringBuilder(),digits=new StringBuilder();
for(char ch:s.toCharArray()){
if(Character.isLetter(ch)){
letters.append(ch);
}
else if(Character.isDigit(ch)){
digits.append(ch);
}
}
int lenLetters=letters.length(),lenDigits=digits.length();
if(Math.abs(lenLetters-lenDigits)>1) return "";
StringBuilder sb=new StringBuilder();
int i=0,j=0;
boolean flag=lenLetters>=lenDigits?true:false; // boolean to decide if we should start with characters or digits
while(i<letters.length()||j<digits.length()){
if(flag&&i<lenLetters) {sb.append(letters.charAt(i++));flag=false;}
if(!flag&&j<lenDigits) {sb.append(digits.charAt(j++));flag=true;}
}
return sb.toString();
}
}
/* should use boolean to decide if we should start with characters or digits
class Solution {
public String reformat(String s) {
int cntLetters=0,cntDigits=0;
StringBuilder letters=new StringBuilder(),digits=new StringBuilder();
for(char ch:s.toCharArray()){
if(Character.isLetter(ch)){
cntLetters++;
letters.append(ch);
}
else if(Character.isDigit(ch)){
cntDigits++;
digits.append(ch);
}
}
if(Math.abs(cntLetters-cntDigits)>1) return "";
StringBuilder sb=new StringBuilder();
if(cntLetters<cntDigits){
StringBuilder tmp=letters;
letters=new StringBuilder(digits);
digits=new StringBuilder(tmp);
}
int i=0,j=0;
boolean flag=true;
while(i<letters.length()||j<digits.length()){
if(flag&&i<letters.length()) {sb.append(letters.charAt(i++));flag=false;}
if(!flag&&j<digits.length()) {sb.append(digits.charAt(j++));flag=true;}
}
return sb.toString();
}
}*/