Write Code vs. Write Poetry: String Character Count (String)
Question: a#3bd#5 -》 aaabddddd..
Idea: Since the number after # may be zero or numbers larger than 9, we need to take care of the corner cases a little bit.
Use a stringbuilder to cache the result and use a pointer to scan from left to right. If it is a letter, append to the stringbuilder; if it is a '#', temporally store the last character in the stringbuilder, pop the last character, count the number to append, append them and move the pointer forward.
Time: O(n) Space: O(1)
Question: a#3bd#5 -》 aaabddddd..
Idea: Since the number after # may be zero or numbers larger than 9, we need to take care of the corner cases a little bit.
Use a stringbuilder to cache the result and use a pointer to scan from left to right. If it is a letter, append to the stringbuilder; if it is a '#', temporally store the last character in the stringbuilder, pop the last character, count the number to append, append them and move the pointer forward.
Time: O(n) Space: O(1)
public StringConvert()
{
String input1="a#3bd#5e#33";
System.out.println(stringExpand(input1));
}
public String stringExpand(String s)
{
if(s==null||s.length()==0)
return s;
StringBuilder builder=new StringBuilder();
for(int i=0;i<s.length();)
{
char c=s.charAt(i);
if(getType(c)==3)
{
builder.append(c);
i++;
}
else
{
int num=0;
char lastC=builder.charAt(builder.length()-1);
int j=i;
for(j=i+1;j<s.length()&&getType(s.charAt(j))==2;j++)
{
num=num*10+(int)(s.charAt(j)-'0');
}
builder.deleteCharAt(builder.length()-1);
for(int k=0;k<num;k++)
builder.append(lastC);
i=j;
}
}
return builder.toString();
}
public int getType(char c)
{
if(c=='#')
return 1;
if(c>='0'&&c<='9')
return 2;
else
return 3;
}
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