Leetcode 6——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".

思路：找出规律，然后按照新字符串的顺序放到新字符串中，注意下标。

class Solution {
    
    public String convert(String s, int numRows) {
        if(numRows<=1||numRows>=s.length())return s;
       
        StringBuffer newString=new StringBuffer();
        int gap=2*numRows-2;//周期数
        int n=numRows;//循环数
        int index;
        
        while(n-->0){
            if(n==numRows-1||n==0){
                for(int i=numRows-n-1;i<s.length();i=i+gap){
                    newString.append(s.charAt(i));
                }
            }
            else{
                for(int i=numRows-n-1;i<s.length();i=i+gap){
                    newString.append(s.charAt(i));
                    if((index=(i/gap*gap+2*numRows-(i%gap)-2))<s.length())
                    newString.append(s.charAt(index));
                }
            }
        }
        return newString.toString();
            
    }
}