LeetCode-6-ZigZag Conversion

算法描述：

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 s, int numRows);

Example 1:

Input: s = "PAYPALISHIRING", numRows = 3
Output: "PAHNAPLSIIGYIR"

Example 2:

Input: s = "PAYPALISHIRING", numRows = 4
Output: "PINALSIGYAHRPI"
Explanation:

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

解题思路：

对于这个题目，网上查了很久，终于找到一个比较好的解题思路。

以Example2为例，从P到I的距离为 2*numRows -2 = 6。也就是说每六个元素为一个循环，因此可以为6取模作为元素所在行的索引。其中，对于索引值小于numRows的直接用索引值作为行号，而大于等于的值则采用补数作为索引值。

    string convert(string s, int numRows) {
        if(numRows <=1) return s;
        string results;
        vector<string> str(numRows,"");
        for(int i =0; i < s.size(); i++){
            int index = i % (2*numRows -2);
            index = index < numRows? index : 2*numRows -2 - index;
            str[index] += s[i];
        }
        for(int i=0; i < numRows; i++) results += str[i];
        return results;
    }

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 s, int numRows);

Example 1:

Input: s = "PAYPALISHIRING", numRows = 3
Output: "PAHNAPLSIIGYIR"

Example 2:

Input: s = "PAYPALISHIRING", numRows = 4
Output: "PINALSIGYAHRPI"
Explanation:

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