ZigZag Conversion

The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

P   A   H   N
A P L S I I G
Y   I   R

And then read line by line: "PAHNAPLSIIGYIR"

Write the code that will take a string and make this conversion given a number of rows:

string convert(string text, int nRows);

convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".

对于字符串操作 深有体会 使用+效率低：代码如下：


   public String convert(String s, int nRows) {
         if(s==null||s.length()<=1||nRows<=1)
return s;
int len=s.length();
String sb="";
for(int i=0;i int k=i;
if(k==0||k==nRows-1)
while(k sb+=s.charAt(k);
k+=2*nRows-2;
 
}
else {
while(k  sb+=s.charAt(k);
k+=2*(nRows-i)-2;
if(k>=len)
break;
 sb+=s.charAt(k);
k+=2*i;
 
}
}
}
return sb;
    }
执行时间是565ms

public String convert(String s, int nRows) {
if(s==null||s.length()<=1||nRows<=1)
return s;
int len=s.length();
StringBuilder sb=new StringBuilder();
for(int i=0;i int k=i;
if(k==0||k==nRows-1)
while(k sb.append(s.charAt(k));
k+=2*nRows-2;
 
}
else {
while(k sb.append(s.charAt(k));
k+=2*(nRows-i)-2;
if(k>=len)
break;
sb.append(s.charAt(k));
k+=2*i;
 
}
}
}
return sb.toString();
 
 
}

使用StringBuilder是348ms。