ZigZag Conversion

题目：

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"

.

好吧，不得不承认，自己开始没看懂题目，百度了下才看懂题目，其实就是“之字型”。

题目看懂了后思路就比较直观了，用一个字符串数组来存每一行的数据，边遍历边把数据放到相应的行里去，找个变量来记录当前的行数，因为行数变化有加减两种情况，所以搞个标志位来判断当前的行数应该加还是减，每当行数到最大行或者第一行标志位取反即可。相应代码如下：

public class Solution {
public String convert(String s, int numRows) {
//各种特殊情况的处理，养成入参检查的习惯是很重要！
if (s == null || s.length() == 0 || numRows <= 1) {
return s;
}
String[] strings = new String[numRows];
Arrays.fill(strings,"");//字符串数组初始化，否者会有null输出
int num = 0;
boolean flag = true;//判断行数该加还是该减的标志位
for (int i = 0;i < s.length();i++) {
strings[num] += s.charAt(i);
if (num == 0) {
flag = true;
}
if (num == numRows-1) {
flag = false;
}
num = flag?++num:--num;
}
String s1 = "";
for (int i = 0;i < numRows;i++) {
s1 += strings[i];
}
return s1;
}
}