【leetcode】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   NA P L S I I GY   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".

解决思路：

       对于这个问题，首先要进行分析，如下：

       首先，将这个问题分为三个部分

（1）当位于第一行时，每两个之间相差 2*numRows-2;

（2）当位于中间行i行时，偶数列与奇数列之间相差2*（numRows-1-i），奇数列与偶数列之间相差2*i；

（3）当位于最后一行时，每两个元素之间相差2*numRows-2，因此可以和第（1）中情况合并；

Solution:

public class Solution {    public String convert(String s, int numRows) {        if(numRows == 1 || s.length() <= 1)            return s;        char []res = new char[s.length()];        int i;        int j = 0;        for(int row = 0; row < numRows; ++row)        {            if(row == 0){                i = 0;                while(i < s.length()){                    res[j++] = s.charAt(i);                    i += 2*(numRows-1);                }            }            else if(row == numRows-1){                i = numRows - 1;                while(i < s.length()){                    res[j++] = s.charAt(i);                    i += 2*(numRows-1);                }            }else{                i = row;                while(i < s.length()){                    res[j++] = s.charAt(i);                    i += 2*(numRows - 1 - row);                    if(i < s.length()){                        res[j++] = s.charAt(i);                        i += 2*row;                    }                }            }        }                        return new String(res);            }}

AC:49ms